Chapter 1 Section 1
Science Starts with a Question
•The process of gathering knowledge about the natural world is called science. Asking a question is often the first step in the process of gathering knowledge.
•In Your Own Neighborhood Take a look around your school and your neighborhood. What questions can you ask about your surroundings?
•The World and Beyond The world is a big place. What questions can you ask about deserts, forests, or beaches? What type of plants and animals live in each of these places?
•Earth is not the only place to look for questions. You can look outward to the moon, sun, and the rest of the universe.
Investigation: The Search for Answers
•Research -Find answers to questions by looking up information in reliable sources.
•Observation - Make careful observations to answer questions.
•Experimentation - Perform experiments to learn answers to questions.
Why Ask Why?
•Saving Lives Science helps make cars safer in many ways. These safety measures help save lives.
•Saving Resources Science helps make resources last longer through more-efficient methods of recycling.
•Saving the Environment Science helps protect the environment and makes the world a healthier place.
Scientists Are All Around You
•Meteorologist- A meteorologist is a person who studies the atmosphere.
•Geochemist- A geochemist is a person who specializes in the chemistry of rocks, minerals, and soil.
•Ecologist - An ecologist is a person who studies a community of organisms and their nonliving environment.
•Volcanologist- A volcanologist is a person who studies volcanoes.
•Science Illustrator- A science illustrator is a person who draws scientific diagrams.
Chapter 1 Section 2
What Are Scientific Methods?
•The ways in which scientists answer questions and solve problems are called scientific methods.
Ask a Question
•Asking a question helps focus the purpose of an investigation. Scientists often ask a question after making observations.
•Observation- is any use of the senses to gather information.
•Observations should be accurately recorded so that scientists can use the information in future investigations.
•A Real-World Question Engineers are scientists who put scientific knowledge to practical human use. Engineers create technology.
Technology- is the application of science for practical purposes.
Form a Hypothesis
•Once you have asked a question and made observations, you are ready to form a hypothesis.
Hypothesis- an explanation that is based on prior scientific research or observations that can be tested. (Educated Guess).
•Make Predictions Before scientists test a hypothesis, they often make predictions that state what they think will happen during the actual test of the hypothesis.
Test the Hypothesis
•After you form a hypothesis, you must test it. Testing helps you find out if your hypothesis is correct or not.
•Keep It Under Control One way to test a hypothesis is to do a controlled experiment. A controlled experiment tests one variable at a time. By changing only the variable, scientists can see the results of just that one change.
Data- are pieces of information acquired through observation or experimentation.
Analyze the Results
Once you have your data, you must analyze them to find out whether the results support your hypothesis.
Draw Conclusions
•At the end of an investigation, you must draw a conclusion. Your conclusion can help you decide what you do next.
Communicate Results
•One of the most important steps in an investigation is to communicate your results accurately and honestly.
Chapter 1 Section 3
Measurement
•The International System of Units (SI) is the current name for the metric system. It is used by most scientists and almost all countries. All SI units are based on the number 10.
•Length - The basic SI unit of length is the meter (m). Other SI units of length are larger or smaller than the meter by multiples of 10.
•Area is a measure of how much surface an object has. The units for area are square units, such as square kilometers (km2) and square meters (m2).
•The equation for calculating area is:
Area = Length x Width
A= L x W
•Mass is the amount of matter that something is made of. The kilogram (kg) is basic SI unit for mass.
•Volume - is the amount of space that something occupies.
The volume of liquids are usually given in liters (L) or milliliters (mL). The volume of solids can be given in cubic meters (m3), cubic centimeters (cm3), or cubic millimeters (mm3).
•Density- is the amount of matter in a given volume.
Density can be expressed in grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3).
The equation for calculating density is:
Desity= Mass/Volume
D= M/V
Writing Numbers in Scientific Notation
•Scientific notation is a method of expressing a quantity as a number multiplied by 10 to the appropriate power.
•For example, the measurement 300,000,000 m/s can be written as 3.0 ´ 108 m/s in scientific notation.
•The same is true of small measurements. For example, the quantity 0.0015 kg can be written as 1.5 ´ 10-3 in scientific notation.
CHAPTER 10 WAVES
SECTION 1
•A wave is any disturbance that transmits energy through matter or empty space.
•Energy can be carried away from its source by a wave. However, the material through which the wave travels does not move with the energy.
•Vibrations and Waves A repetitive, back-and-forth motion of an object is called a vibration.
•Vibrations set up wave disturbances in a material, and the waves spread away from the source of vibration.
•A vibrating particle passes its energy to a nearby particle. In this way, energy is transmitted through a material.
•A medium is a substance through which a wave can travel.
•Sound waves, water waves, and seismic waves all need a medium through which to travel.
•Energy Transfer Without a Medium Visible light waves, microwaves, radio waves, and X rays are examples of waves can transfer energy without going through a medium.
•These waves are electromagnetic waves. Although electromagnetic waves do not need a medium, they can go through matter.
•Transverse Waves are waves in which the particles vibrate perpendicularly to the direction the wave is traveling.
•Transverse waves are made up of crests and troughs.
•Water waves, waves on a rope, and electromagnetic waves are examples of transverse waves.
•Longitudinal Waves are waves in which the particles vibrate back and forth along the path that the waves moves.
•Longitudinal waves are made up of compressions and rarefactions.
•Waves on a spring are longitudinal waves.
•Sound Waves are longitudinal waves. Sound waves travel by compressions and rarefactions of air particles.
•Surface Waves: Combinations of Waves A transverse waves and a longitudinal wave can combine to form a surface wave.
•Surface waves look like transverse waves, but the particles of the medium move in circles rather than up and down.
CHAPTER 10 SECTION 2
•The amplitude of a wave is the maximum distance that the particles of a medium vibrate from their rest position.
A wave with a large amplitude carries more energy than a wave with a small amplitude does.
•A wavelength is the distance between any point on a wave to an identical point on the next wave.
•A wave with a shorter wavelength carries more energy than a wave with a longer wavelength does.
•Frequency is the number of waves produced in a given amount of time. Frequency is usually expressed in hertz (Hz). One hertz equals one wave per second.
•Wave Speed is the speed at which a wave travels.
Chapter 16 Stars
Section 1
•If you look closely, you may notice that not all stars are the same color.
•Because a blue flame is hotter than a yellow or red flame, we can conclude that blue stars are hotter than yellow or red stars.
•A star is made of different elements in the form of gases. The center of a star is dense, but the outer layers are less dense and make up the star’s atmosphere.
•The different gases in the atmosphere of a star absorb different wavelengths of light.
•The light from a star indicates which elements make up that star.
•The Colors of Light A prism breaks white light into a rainbow of colors called a spectrum.
•An instrument called a spectrograph is used to break a star’s light into a spectrum.
•The spectrum of a star gives information about the composition and temperature of a star.
•Star Emission lines are lines made when certain wavelengths,of light, or colors, are given off by hot gasses.
•Each elements produces a unique set of emission lines, which allows them to be used to identify the elements in a star.
•Differences in Temperature Stars are classified by how hot they are.
•Stars are also classified on the basis of brightness. The brightest stars have a negative score, or magnitude, and the brightest stars have a positive magnitude.
•Apparent Magnitude -The brightness of a star as seen from Earth is called apparent magnitude.
•Absolute Magnitude - The actual brightness of a star. The sun has an absolute magnitude of 4.8, but because it is so close to the Earth, its apparent magnitude is -26.8.
•Astronomers use light-years to measure the distances from Earth to the stars. A light year is the distance that light travels in a year.
•Parallax is the apparent shift in the position of an object when viewed from different locations. Measuring parallax enables scientists to calculate the distance between a star and the Earth.
•Stars that are closer to Earth seem to shift more than those that are farther away.
•The Apparent Motion of Stars If you look at the night sky long enough, the stars appear to move.This is due to the rotation of the Earth.
•The Actual Motion of Stars Each star really is moving in space. Their actual movements, however, are difficult to see because they are so far away. The movements we observe each night are due to the Earth’s rotation.
Section 2
The Beginning and End of Stars
•A star enters the first stage of its life cycle as a ball of gas and dust. Gravity pulls the gas and dust together, and hydrogen changes to helium in a processes called nuclear fusion.
•Stars usually lose material slowly, but sometimes they can lose material in a big explosion. Much of a star’s material returns to space, where it sometimes forms new stars.
•Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and age. A star’s classification can change as it ages.
•Main-Sequence Stars After a star forms, it enters the second and longest stage of its life cycle known as the main sequence. Energy is generated in the core as hydrogen atoms fuse into helium atoms.
•Giants and Supergiants After the main-sequence stage, a star can enter the third stage of its life cycle. As the center of the star shrinks, the atmosphere of the star grows very large and cools.
•A red giant is a large, reddish star late in its life cycle.
•Red giants can be 10 times bigger than the sun. Supergiants are a t least 100 times bigger than the sun.
White Dwarf is a small, hot, dim star that is the leftover center of an old star.
•White dwarfs have run out of hydrogen and no longer fuse hydrogen to make helium. They may take billions of years to cool completely, and continue to shine.
•The Hertzprung-Russell diagram, or H-R Diagram, is a graph that shows the relationship between a star’s surface temperature and absolute magnitude.
Supernova is a gigantic explosion in which a massive star collapses and throws its outer layers into space. Supernovas can be brighter than an entire galaxy for several days.
•Neutron Star is a star that has collapsed to the point at which all of its particles are neutrons. If a neutron star is spinning, it is called a pulsar.
•Black Holes If the leftovers of a supernova are more than 3 times the mass of the sun, they may collapse further to form a black hole. A black hole is an object that is so massive and dense that even light cannot escape its gravity.
Section 3 Galaxies
•A galaxy is a collection of stars, dust, and gas held together by gravity.
Types of Galaxies
•Spiral Galaxies have a bulge at the center and spiral arms.
•The Milky Way It is difficult to view or own galaxy, the Milky Way. Astronomers think that our solar system is in a spiral galaxy.
•Elliptical Galaxies -About one-third of all galaxies are simply massive blobs of stars. These are called elliptical galaxies. They may be huge or rather small, and contain mostly older stars.
•Irregular Galaxies -Galaxies that do not fit into any other class are called irregular galaxies. As their name suggests, they have an irregular shape.
•A large cloud of gas and dust in interstellar space is called a nebula. New stars are often born within nebulas.
•Globular Cluster is a tight group of stars that looks like a ball and contains up to 1 million stars.
•An Open Cluster is a close grouping of stars usually located along the spiral disk of a galaxy.
A very luminous object that generates energy at a high rate is called a quasar. Quasars are thought to be the most distant objects in the universe, and may be caused by massive black holes.
Section 4 Formation of the Universe
•Cosmology is the study of the origin, structure, and future of the universe.
•Galaxy Movement To understand how the universe formed, scientists study the movement of galaxies.
•The theory that the universe began with a tremendous explosion is called the Big Bang Theory.
•According to the theory, about 14 billion years ago the contents of the universe were compressed into an extremely small volume.
•Suddenly the universe expanded in a rapid explosion, and matter came together to form galaxies.
•Cosmic Repetition - The objects in the universe are not simply scattered in a random pattern. There is a loose structure repeated over and over again.
•Every object in the universe is part of a larger system. Earth is part of a solar system, which is part of the Milky Way, which is part of a cluster of galaxies.
•Scientists believe that planetary systems are common in the universe.
How Old Is the Universe?
•By measuring the distance between Earth and various galaxies, scientists can predict the rate of expansion and calculate the age of the universe.
•The ages of old, nearby stars can also give clues to the age of the universe. The universe must at least be as old as the oldest stars it contains.
A Forever Expanding Universe
•The expansion of the universe depends on the amount of matter it contains. With enough matter, gravity might bring a halt to the expansion. The universe could start collapsing.
•Scientist now think that there may not be enough matter in the universe to halt the expansion. If so, the universe will continue to expand forever and become cold and dark as all the stars eventually die.
Chapter 17
Section 1 The Nine Planets
•Scientists use the astronomical unit to measure distances in space. One astronomical unit (AU) is the average distance between the sun and Earth, or approximately 150,000,000 km.
•The solar system is divided into the inner and outer solar systems.
•The Inner Planets The planets closest to the sun include Mercury, Venus, Earth, and Mars. These planets are more closely spaced than the outer planets, and have rocky surfaces.
•The Outer Planets The outer planets include Jupiter, Saturn, Uranus, Neptune, and Pluto.
Section 2 The Inner Planets
•The inner planets are also called the terrestrial planets because, like Earth, they are very dense and rocky.
•The inner planets include one of the hottest places in the solar system, and the only planet known to support life.
Mercury: Closest to the Sun
•Mercury is a very hot, small planet. Mercury’s period of rotation, or day-length, is almost 59 Earth days, while its period of revolution, or year, is only 88 Earth days.
•This means Mercury’s year is only 1.5 Mercurian days long.
•Venus is similar to the earth in size and composition. However, the sun rises in the west because it has a retrograde rotation.
•Planets that rotate like the Earth and sun, in a counterclockwise direction, have a prograde rotation.
•Planets that rotate opposite the Earth, in a clockwise direction, have a retrograde rotation.
•The Atmosphere of Venus is mostly carbon dioxide which traps the sun’s heat, giving Venus the hottest surface temperature of any planet.
•The atmosphere of Venus is the densest of any terrestrial planet, and contains some of the most destructive acids known.
•Mapping Venus’s Surface The Magellan spacecraft mapped the surface of Venus by using radar waves, revealing volcanoes.
Earth: An Oasis in Space
•Water on Earth Earth is warm enough to keep most of its water from freezing and cool enough to keep its water from boiling away. Liquid water is important to life on Earth.
•The Earth from SpaceSatellites are used tostudy the Earth to betterunderstand how global systems interact.
Mars: Our Intriguing Neighbor
•The Atmosphere of Mars Mars has a thin atmosphere with low air pressure. It is also the furthest from the sun of the inner planets. This makes Mars a cold planet.
•Water on Mars Liquid water cannot exist on Mars’s surface today, but surface features on the planet look like water was once present.
•This means Mars might have been warmer with a thicker atmosphere in the past.
•Where Is the Water Now? Mars has two polar icecaps made of frozen water and frozen carbon dioxide. Many scientists think that there is more frozen water beneath the Martian soil.
•Martian Volcanoes Mars has only two large volcanic systems, one of which includes the largest mountain in the solar system: Olympus Mons.
Section 3 The Outer Planets
Jupiter: A Giant Among Giants
•The gas giants are planets that have deep, massive atmospheres rather than hard rocky surfaces. Except for Pluto, all of the outer planets are gas giants.
Jumbo Sized Jupiter is the largest planet in our solar system. It is mostly hydrogen and helium, and radiates more energy than it receives from the sun.
Saturn: Still Forming
•Saturn is the second largest planet in the solar system. Like Jupiter, it is made mostly of hydrogen and helium and gives off more energy than it receives from the sun.
•Scientists think Saturn gets its extra energy from helium falling out of the atmosphere and sinking to the core. In this way, Saturn is still forming.
•The Rings of Saturn All the gas giants have rings, but Saturn’s rings are the largest. They are made of icy particles.
Uranus: A Small Giant
•The atmosphere of Uranus (Yoor uh nuhs) is mainly hydrogen and methane, which makes the planet appear to be blue-green in color.
Neptune: The Blue World
•Neptune was not discovered until 1846, but its existence was predicted by irregularities observed in Uranus’ orbit.
•The Atmosphere of Neptune is similar to that of Uranus, but Neptune has belts of clouds that are much more visible.
Pluto: The Mystery Planet
•A Small World Less than half the size of Mercury, Pluto is the smallest planet in the solar system.
•A True Planet? BecausePluto is so small andunusual, some scientiststhink that is should notbe classified as a planet.Some scientists classifyPluto as a large asteroidor comet.
Section 4 Moons
•Natural or artificial bodies that revolve around other bodies such as planets are called satellites.
•Except for Mercury and Venus, all of the planets in our solar system have natural satellites called moons.
•Lunar rocks brought back during the Apollo missions were found to be about 4.6 billion years old. Scientists used this information to age the solar system itself to be 4.6 billion years old.
•The Surface of the Moon The surfaces of bodies that have no atmospheres, such as the moon, preserve a record of almost all of the impacts that the bodies have ever had.
•Lunar Origins Until rock samples from the moon were brought back, the origins of the moon were a mystery.
Scientists now believe the moon formed from a collision with a Mars-sized object that threw part of the Earth into orbit around itself.
•Phases of the Moon The different appearances of the moon due to its changing position are called phases.
•Waxing and Waning When the moon is waxing, the sunlit fraction that we can see from Earth is getting larger. When the moon is waning, the sunlit fraction is getting smaller.
•Half of the moon is always lit by the sun, but the amount we can see from Earth changes due to the changing position of the moon relative to the sun and Earth.
•Eclipses When the shadow of one celestial body falls on another, an eclipse occurs.
•Solar Eclipses During a total solar eclipse, the disk of the moon completely covers the disk of the sun, as shown below.
•Lunar Eclipses During a lunar eclipse, the moon passes through the Earth’s shadow.
•The Tilted Orbit of the Moon You don’t see a solar and lunar eclipse every month because the moon’s orbit around the Earth is tilted.
•The Moons of Mars Mars’s two moons, Phobos and Deimos, are small, oddly shaped satellites. Scientists think these two moons are asteroids caught in Mars’s gravity.
•The Moons of Jupiter Jupiter has dozens of moons. Liquid water may be beneath the surface of the moon Europa.
•Jupiters’s four largest moons were discovered in 1610 by Galileo. The largest moon, Ganymede, is larger than Mercury.
•The Moons of Saturn Like Jupiter, Saturn has dozens of moons. Most of these moons are small bodies of frozen water but some contain rocky material.
•The Casini spacecraft revealed a hazy orange atmosphere around Titan, Saturn’s largest moon. Titan’s atmosphere may be similar to Earth’s early atmosphere.
•The Moons of Uranus Uranus has several moons. Uranus’s largest moons are made of ice and rock and are heavily cratered.
•The Moons of Neptune Neptune has several known moons, only one of which is large. The large moon has a thin atmosphere of nitrogen and has a retrograde (backward) orbit.
•The Moon of Pluto Pluto’s only known moon is Charon. Charon’s orbit is tilted relative to Pluto’s orbit.
Section 5 Smaller Bodies in te Solar System
Comets
•A small body of ice, rock, and cosmic dust loosely packed together is called a comet. Some scientists refer to comets as “dirty snowballs.”
•Comets are probably left over from the time when the planets formed.
•Comet Tails When a comet passes close enough to the sun, solar radiation heats the ice so that the comet gives off gas and dust in the form of a long tail.
Asteroids
•Small, rocky bodies that orbit the sun are called asteroids. They range in size from a few meters to more than 900 km in diameter.
•Most asteroids exist in the asteroid belt, a region of the solar system between the orbits of Mars and Jupiter.
Meteoroids
•A meteoroid is a small, rocky body that revolves around the sun. They are similar to but much smaller than asteroids.
•Meteor Showers You can see a large number of meteors when the Earth passes through the dusty debris of comets.
•A meteor is a bright streak of light caused by a meteoroid falling through Earth’s atmosphere. These “shooting stars” are dust- to pebble-sized particles burning up from friction.
•A meteoroid that falls through the atmosphere without burning up completely and strikes the ground is called a meteorite.
•Like asteroids, meteorites have different compositions. There are three major types of meteorites: stony, metallic, and stony-iron.
Chapter 19 Heridity
Section 1 Mendel and His Peas
•Gregor Mendel was born in 1822 in Heinzendorf, Austria.
•At age 21, Mendel entered a monastery. He performed many scientific experiments in the monastery garden.
•Mendel discovered the principles of heredity, the passing of traits from parents to offspring.
•Mendel used garden pea plants for his experiments.
•Self-Pollinating Peas have both male and female reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower.
•When a true-breeding plant self pollinates, all of the offspring will have the same trait as the parent.
•Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant.
•Characteristics and Traits of Pea Plants Mendel studied only one pea characteristic at a time. A characteristic is a feature that has different forms in a population.
•Different forms of a characteristic are called traits.
•Mix and Match Mendel was careful to use plants that were true breeding for each of the traits he was studying. By doing so, he would know what to expect if his plants were to self-pollinate.
•Mendel crossed pea plants to study seven different characteristics.
•Mendel got similar results for each cross. One trait was always present in the first generation, and the other trait seemed to disappear.
•Mendel called the trait that appeared the dominant trait. The trait that seemed to fade into the background was called the recessive trait.
•To find out more about recessive traits, Mendel allowed the first-generation plants to self-pollinate.
•In each case some of the second-generation plats had the recessive trait.
•Ratios in Mendel’s Experiments The recessive trait did not show up as often as the dominant trait.
•Mendel decided to figure out the ratio of dominant traits to recessive traits.
•Gregor Mendel – Gone But Not Forgotten Mendel realized that his results could be explained only if each plant had two sets of instructions for each characteristic.
•Mendel’s work opened the door to modern genetics.
Section 2 Traits and Inheritance
•Mendel knew that there must be two sets of instructions for each characteristic.
•The instructions for an inherited trait are called genes.
•The different forms (often dominant and recessive) of a gene are alleles.
•Dominance occurs when certain alleles mask the expression of other alleles.
•A recessive trait or allele is expressed only when two recessive alleles for the same characteristic are inherited.
•Phenotype An organism’s appearance is known as its phenotype. Genes affect the phenotype.
•Genotype The combination of inherited alleles together form an organism’s genotype.
• A plant with two dominant or two recessive alleles is said to be homozygous.
•A plant that has the genotype Pp is said to be heterozygous.
•Punnett Squares are used to organize all the possible genotype combinations of offspring from particular parents.
•Probability is the mathematical chance that something will happen.
•Probability is most often written as a fraction of percentage.
•Genotype Probability To have white flowers, a pea plant must receive a p allele from each parent. Each offspring of a Pp Pp cross has a 50% chance of receiving either allele from either parent. So, the probability of inheriting two p alleles is 1/2 ´ 1/2, which equals 1/4, or 25%.
•Incomplete Dominance Researchers have found that sometimes one trait is not completely dominant over another.
•One Gene, Many Traits Sometimes one gene influences more than one trait.
•Many Genes, One Trait Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together.
•Genes aren’t the only influences on traits. A combination of things determine an individual’s characteristics.
•Your environment also influences how you grow.
•Lifestyle choices can also affect a person’s traits.
Chapter 9
Section 1 - Motion
Describing Motion
•In science, motion is the change of position of an object relative to a reference point.
•A reference point is an object that appears to stay in place.
•Position -To accurately describe the position of an object, you must use a reference point, a distance, and a direction.
•When you describe the motion of an object, you would describe how the object’s distance or direction or both changed relative to the reference point.
•Speed -is the distance traveled divided by the time taken to travel that distance.
•Speed is important in describing motion because it tells how fast an object is moving away from its beginning position.
The units for speed are often m/s, but can be any distance unit divided by a time unit.
•Direction of Motion Speed and direction of motion are combined when describing an object’s velocity.
•Velocity is a quantity that tells both how fast an object is moving (its speed) and which way it is going (its direction of motion).
•Acceleration: Sometimes the velocity of an object changes. The change in velocity over time is called acceleration.
•Acceleration can be a change in speed, a change in direction, or both.
•The most common units of acceleration are meters per second , or (m/s).
Forces Changing Motion
•A force is any push or pull on an object.
•The SI unit for force is the newton (N).
•When a force is applied on an object, the object’s motion can change.
•Finding Net Force A net force is the combination of all of the forces acting on an object.
•If two forces are in the same direction, you add the forces to calculate the net force.
•If the forces are in opposite directions, you must subtract the forces to find the net force.
•If the net force on an object is 0 N, the forces on the object are said to be balanced.
•But if the net force is not equal to 0 N, the forces on the objects are unbalanced.
•Whether the forces are balanced or unbalanced determines whether the motion of an object changes.
•Balanced Forces: No Change in Motion If the forces on an object are balanced, the motion of the object will not change.
•The object will not increase or decrease in speed, or change direction.
•If an object is standing still, it will remain so.
•Increasing Speed with Net Force If the forces on an object are unbalanced, the motion of the object will change.
•A net force on a nonmoving object will cause the object to move in the direction of the net force.
•Decreasing Speed with Net Force A net force can also slow down an object that is already moving.
Friction Opposes Motion
•Friction is a contact force that opposes motion when two surfaces are touching.
•There are two kinds of friction: static and kinetic.
•Static Friction When a force is applied to an object but does not cause the object to move, static friction occurs.
•Kinetic Friction Kinetic friction is friction between moving surfaces.
Section 2- Gravity
Gravity is a Universal Force
•Gravity is a result of mass and all matter is affected by gravity. Because gravity affects all matter, it is a universal force.
•All objects experience an attraction toward all other objects.
Weight as a Measure of Gravitational Force
•Weight is a measure of the gravitational force on an object.
•When you see or hear the word weight, it usually refers to Earth’s gravitational force on an object.
•Weight can also be a measure of the gravitational force exerted on objects by the moon or other planets.
•Units of Weight and Mass Gravity is a force, and weight is a measure of gravity. So, weight is also measured in newtons.
•The SI unit of mass is the kilogram (kg). Mass is often measured in grams (g) and milligrams (mg) as well.
•The Differences Between Weight and Mass Weight changes when gravitational force changes.
•Mass is the amount of matter in an object. An object’s mass does not change.
•Because mass and weight are constant on Earth, the terms weight and mass are often used to mean the same thing.
•Gravity and Acceleration Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects.
•Acceleration Due to Gravity, for every second that an object falls, the object’s downward velocity increases by 9.8 m/s.
•Velocity of Falling Objects You can calculate the change in velocity with the following equation:
∆v = g X´ t
•If an object starts at rest, this equation yields the velocity of the object after a certain time period.
Air Resistance and Falling Objects
•Air resistance is the force that opposes the motion of objects through air.
•The amount of air resistance acting on an object depends on the size, shape, and speed of the object.
•Acceleration Stops at the Terminal Velocity As the speed of a falling object increases, air resistance increases.
The upward force of air resistance continues to increase until it is equal to the downward force of gravity. The object then falls at a constant velocity called the terminal velocity.
