Physics: The Study of Matter and Forces in Our World

Physical Physics The Study of How Matter Behaves Physics is the branch of science that concerns the behavior of matter in our world—the forces that cause matter to behave as it does. Physics helps to explain how cellular molecules can move from a lower concentration in an organism to a higher one, how ocean tides occur, and how matter exists in the states of a solid, liquid, or gas. (page 555)

Physical Science Physics The Study of How Matter Behaves Many of the properties and behaviors of matter can be explained by force and energy. A force shows the presence of energy in an environment. Energy is the capacity to do work. The area of physics that deals with forces, energy, and their effect on bodies is mechanics. (page 555)

Physical Science Physics The Study of How Matter Behaves

Physical Science Physics Mechanics The study of mechanics was one of the first sciences developed. Ancient Greek philosopher and scientist Aristotle theorized that heavy bodies fall faster than light bodies. This theory was proved false in the early 17th century by Italian scientist and mathematician Galileo, who dropped items of different weights from the leaning tower of Pisa. (page 556)

Physical Science Physics Mechanics

Physical Science Physics Mechanics The force acting upon the objects was not fully understood, however, until Englishman Sir Isaac Newton formulated laws of gravity and motion that explained how different forces act on objects. (page 556)

Physical Science Physics Mechanics

Physical Science Physics The Force of Gravity Gravity is the most commonly experienced of all forces in nature. The presence of gravity was first proposed by Newton when he observed the motion of an apple falling from a tree. On the basis of this simple observation, he developed the Law of Universal Gravitation, which holds that every body having a mass exerts an attractive force on every other body having a mass in the universe. (page 556)

Physical Science Physics The Force of Gravity The strength of the force depends on the masses of the objects and the distance between them. (Mass is the measure of the amount of matter in an object.) Thus, the apple's falling illustrates the gravitational pull (attraction) of the larger Earth on the smaller apple. The Law of Universal Gravitation also explains how the planets, attracted by the much larger Sun, remain in their orbits as they revolve around it. (page 556)

Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Inertia A body remains at rest or continues in a state of uniform motion unless a force acts on it. For example, when you drive a car and suddenly jam on the brakes, you continue to move forward. This is because your body's tendency is to remain in the same state of uniform motion (moving forward). The brakes were applied to the car, so its uniform motion was changed. (page 556)

Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Applied Force A body's change in speed and direction is proportional to the amount of force applied to it. For example, the vanes on a windmill, which move by the force of the wind, will accelerate according to the speed and direction of the wind that drives them. (page 556)

Physical Science Physics NEWTON'S THREE LAWS OF MOTION The Law of Action and Reaction For every action there is an equal but opposite reaction force. For example, a gun's muzzle kicks backward when a bullet is discharged from it. (page 556)

Physical Science EXERCISE 1 Laws of Force and Motion (page 557) Directions: Identify the following statements as (G) illustrating Newton's Law of Universal Gravitation, (I) applying to the Law of Inertia, (AF) applying to the Law of Applied Force, or (AR) applying to the Law of Action and Reaction. 1. ____ A ball on a pool table rebounds off another ball it just hit. 2. ____ A rocket is propelled upward by the powerful downward discharge of exhaust gases. 3. ____ A bullet fired into the air eventually falls to the ground. 4. ____ A pendulum in a clock, once set in motion, continues to swing, thereby regulating the clock's movement. 5. ____ A jet airplane, upon landing, lowers the flaps on its wings. The flaps create drag, a force that reduces lift and helps the plane to slow down.

Physical Science EXERCISE 2 (page 557) The Force of Gravity Directions: Read the paragraph below and answer the questions that follow. An astronaut weighs in before blast-off. He weighs only a fraction of his original weight when he steps on a scale on the moon. Journeying to Jupiter, he finds that his weight has increased several times over his original weight. 1. How may these changes in weight be best explained? (1) the amount of force each planetary body exerts as the astronaut weighs himself (2) the distance from the Sun of the planetary bodies on which he weighs himself (3) changes in the atmospheric pressure on the different heavenly bodies (4) the amount of calories consumed during the flight (5) the duration of time that elapsed between weigh-ins 2. What do you estimate the weight change for the same astronaut would be if he were to land on Mercury?

Physical Science Work, Energy, and Power According to physics, work occurs when a force succeeds in moving an object it acts upon. For example, a person who lifts a 50-pound weight one foot off the floor is performing work. For work to be performed, the movement of the object must be in the same direction as the force—in this case vertical. (page 558)

Physical Science Work, Energy, and Power (page 558) Work may be expressed as any force unit times any distance unit and may be written as follows: W = FxD The amount of work done is the amount of force multiplied by the distance moved. In the preceding example, 50 foot-pounds of work is done when 50 pounds are lifted one foot: 50 lb x 1 ft = 50 ft lb

Physical Science Work, Energy, and Power Energy is required to do work. In the example above, muscular energy is illustrated in the form of a body that is capable of doing work. Energy may be classified as either kinetic or potential energy.(page 558)

Physical Science Work, Energy, and Power Kinetic energy is energy possessed by a body in motion. The form of energy shown by a moving train is kinetic energy. (page 558)

Physical Science Work, Energy, and Power Potential energy is energy that is stored or is available for use by a body. For example, coal has potential energy that is released only when it is burned. A boulder positioned on a hilltop has potential energy before it is released. When the boulder is pushed, its potential energy becomes kinetic. (page 558)

Physical Science Work, Energy, and Power Power is the rate at which work is done. Power is generally measured in horsepower, which is equal to 550 foot-pounds per second or 33,000 footpounds per minute. (page 558)

Physical Science The Law of Conservation of Energy The Law of Conservation of Energy holds that all of the energy of the universe is conserved. The capacity for energy to do work can be changed from one kind to another, but it cannot be lost. This principle can be illustrated in the following example of energy generated from a waterfall. (page 558)

Physical Science The Law of Conservation of Energy Water possesses potential energy. When water moves rapidly in a downward motion, drawn by the pull of gravity, the potential energy is changed into kinetic energy. Kinetic energy from a waterfall can be harnessed to power a turbine, a rotary engine, creating rotational energy. This is sufficient to generate electrical energy, which in turn is converted into light and heat energy, which we use in our homes. The initial potential energy has been changed into five different forms. (page 558)

Physical Science EXERCISE 3 Forms of Energy (page 559) Directions: Identify the following statements as either demonstrating kinetic energy (K) or demonstrating potential energy (P). 1. ____ a strong west wind blowing across a region 2. ____ a stick of unlit dynamite 3. ____ a hamburger 4. ____ a waterfall

Physical Science EXERCISE 4 Types of Energy (page 559) Directions: Read the following definitions of the five types of energy. Then choose the best answers for the questions below. nuclear energy - energy from splitting an atom or fusing atoms chemical energy - energy from the reaction of two or more substances combining with one another electrical energy- energy from an electric current solar energy - energy from the heat of the Sun steam energy - energy from steam pressure

Physical Science EXERCISE 4 Types of Energy (page 559) 1. Which form of energy results from the fission of uranium-235 nuclei that is used to generate electrical power? (1) nuclear energy (2) chemical energy (3) electrical energy (4) solar energy (5) steam energy

Physical Science EXERCISE 4 Types of Energy (page 559) 2. Which form of energy results from the ignition of a gas and air mixture and powers a car? (1) nuclear energy (2) chemical energy (3) electrical energy (4) solar energy (5) steam energy

Physical Science Simple Machines A machine is a device that transmits or multiplies force. A machine operates on the principle of a little force as being applied through a great distance and a great resistance being overcome through a short distance. (page 560)

Physical Science Simple Machines The lever

Physical Science Simple Machines A lever is a simple machine used to perform work by lifting a great weight. A lever is just a bar that is free to pivot on its support (called a fulcrum). Through the use of a lever, for example, a 1,000-pound weight can be lifted with relatively little effort (force). (page 560)

Physical Science Simple Machines (page 560) The illustration above shows that it would take 100 pounds of force for a person to lift a 1,000-pound weight positioned 1 foot from the fulcrum when the lever bar is 10 feet long. This may be expressed as follows: 1,000 lbx1 ft = 100lbx10ft

Physical Science Simple Machines In this case a relatively small force (100 lb) applied at a great distance from the object (10 ft) is able to overcome great resistance (1,000 lb). According to this principle the greater the distance between the fulcrum and the applied force, the less force required to perform the work. (page 560)

Physical Science Simple Machines The wheelbarrow, the crowbar, the pulley, and the inclined plane are simple machines. Complex machines are made up of more than one simple machine. (page 560)

Physical Science EXERCISE 5 Simple Machines (page 561) Directions: Choose the best answer for each of the following questions. 1. According to the principle that a little force applied through a great distance can overcome great resistance, which would be most likely to happen if the lever bar in the preceding illustration is increased to 20 feet in length and the weight remained at the end of the bar?

Physical Science EXERCISE 5 Simple Machines (page 561) (1) The effort to lift the weight would increase to 150 pounds of applied force. (2) The effort to lift the weight would remain at 100 pounds of applied force. (3) The effort would be decreased by half, to 50 pounds of applied force. (4) The resistance of the weight would double. (5) The resistance of the weight would triple.

Physical Science EXERCISE 5 Simple Machines (page 561) 2. What are some other types of household items that could be considered levers? (Hint: Any tool that makes the job easier is likely a lever.)

Physical Science The Nature of Heat and Energy Today we know that heat is the result of the random motion of molecules. It is nothing more than energy itself. One theory of physics that has contributed greatly to our understanding of the phenomenon of heat is kinetic theory, a basic theory that explains how different states of matter can exist. (page 561)

Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter According to the Kinetic Theory of Matter, matter exists in three states— solid, liquid, or gas. A fourth state, plasma, is an ionized gas; the Sun is made up of plasma. The form, or phase, of matter is determined by the motion of the molecules within it.(page 561)

Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter

Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter Solids are composed of atoms or molecules in limited motion. These atoms or molecules are in direct contact with one another, allowing little or no space for random movement. The attractive forces of the particles keep the solid intact and give the solid its definite shape and structure. (page 561)

Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter In liquids, individual atoms or molecules are able to move past one another into new positions, giving this form of matter its fluidity. Cohesive forces hold liquids intact. (page 561)

Physical Science The Nature of Heat and Energy The Kinetic Theory of Matter Gases are substances in which the individual atoms or molecules are in constant random motion. The motion, or kinetic energy, increases along with an increase in temperature. Molecules are unable to hold together, and this property gives gases the ability to flow or spread out to fill the container in which they are placed. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter The state of matter depends on its heat content. Temperature is a measure of heat intensity. The change from one state of matter to another involves the addition or subtraction of a certain amount of heat per gram of substance. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter For example, at 32 degrees Fahrenheit, water, a liquid, changes to ice, a solid. When the temperature is raised above 32 degrees Fahrenheit, the ice, a solid, changes to water, a liquid. At temperatures at or above 212 degrees Fahrenheit, the boiling point of water, the water changes to steam, a gaseous state. Impurities in water affect its freezing point. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Certain materials expand when their temperatures are raised and shrink when they are lowered. Liquids expand more noticeably than solids, but gases expand even more. The mercury thermometer employs this principle. Temperature can be measured in degrees centigrade or degrees Fahrenheit. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter On the centigrade (or Celsius) scale, 0 degrees represents the freezing point of water, and 100 degrees is the boiling point. On the Fahrenheit scale, 32 degrees represents the freezing point of water, and 212 degrees is the boiling point. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Temperature is measured in degrees by thermometer, and heat is measured by the calorie or British Thermal Unit (BTU). A calorie is the amount of heat needed to raise one gram of water one degree centigrade. The BTU is the amount of heat required to raise one pound of water 1 degree Fahrenheit. (page 562)

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter

Physical Science The Nature of Heat and Energy Heat, Temperature, and the States of Matter Heat is transferred by three methods. The first is called conduction, the transfer of heat between objects that are in direct contact. You have experienced this whenever you have picked up a hot item, such as a handle on a heated pan. The second method is convection. (page 562)

Physics: The Study of Matter and Forces in Our World