Unit 3 pp #1 7th grade
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Transcript of Unit 3 pp #1 7th grade
Section 1 What is Energy?Chapter 19
Energy and Work: Working Together
• In science, energy is the ability to do work.
• Work is done when a force causes an object to move in the direction of the force.
• A tennis player does work on a racket by exerting a force on it. The racket does work on the ball.
Section 1 What is Energy?Chapter 19
• When one object does work on another, energy is transferred from the first object to the second.
• This energy allows the second object to do work.
• So, work is a transfer of energy.
Energy and Work: Working Together, continued
Section 1 What is Energy?Chapter 19
• Like work, energy is expressed in units of joules (J).
• There are many different kinds of energy, and all can be measured and compared.
Energy and Work: Working Together, continued
Section 1 What is Energy?Chapter 19
Kinetic Energy
• Kinetic energy is the energy of motion.
• All moving objects have kinetic energy.
• Kinetic energy can be used to do work. For example, kinetic energy allows a hammer to work on a nail.
Section 1 What is Energy?Chapter 19
• Mass and Speed The amount of kinetic energy that a moving object has depends on the object’s mass and speed.
• The faster an object is moving, the more kinetic energy it has.
• The more mass an object has, the greater its kinetic energy.
Kinetic Energy, continued
Section 1 What is Energy?Chapter 19
• Speed has a greater effect on kinetic energy than mass does.
• A truck with twice the mass of a car but moving at the same speed has twice the amount of kinetic energy.
• But if the speed of the car doubles, its kinetic energy increases by four times.
Kinetic Energy, continued
Section 1 What is Energy?Chapter 19
Potential Energy
• Potential energy is the energy an object has because of its position.
• For example, a stretched bow has potential energy because work has been done to change its shape.
• The energy of that work is turned into potential energy.
Section 1 What is Energy?Chapter 19
Potential Energy, continued
• Gravitational Potential Energy When you lift an object, you are doing work on it.
• You use a force that is working against the force of gravity.
• So, when you lift an object, you transfer energy to it and give it gravitational potential energy.
Potential EnergySection 1 What is Energy?Chapter 19
Section 1 What is Energy?Chapter 19
Potential Energy, continued
• Books on a shelf have gravitational potential energy.
• The amount of gravitational potential energy an object has depends on its weight and height.
• Higher and heavier objects have greater gravitational potential energy.
Section 1 What is Energy?Chapter 19
Mechanical Energy
• Mechanical energy is the total energy of the motion and position of an object.
• Both potential and kinetic energy are types of mechanical energy.
• Mechanical energy can be made up of only potential energy, only kinetic energy, or some of each.
Section 1 What is Energy?Chapter 19
Other Forms of Energy
• All matter is made of particles that are always in random motion.
• Thermal energy is all of the kinetic energy due to the random motion of particles that make up an object.
• Thermal energy is often measured by measuring temperature.
Section 1 What is Energy?Chapter 19
Other Forms of Energy, continued• All matter also has chemical energy.
• Chemical energy is energy stored in chemical bonds. It is a form of potential energy.
• The energy in food is stored as chemical energy.
Section 1 What is Energy?Chapter 19
• Electrical energy is the energy of moving electrons.
• Sound energy is energy created by an object’s vibrations.
• In an amplifier, a vibrating cone causes air particles to vibrate. These vibrating particles transmit sound energy to your ear.
Other Forms of Energy, continued
Section 1 What is Energy?Chapter 19
• Light energy travels in waves called electromagnetic waves.
• Electromagnetic waves can be produced by the vibration of electrically charged particles.
• Some light energy can be seen. Other kinds, such as microwaves and ultraviolet light, can’t be seen by the human eye.
Other Forms of Energy, continued
Section 1 What is Energy?Chapter 19
Other Forms of Energy, continued• Nuclear energy is the energy that comes from
changes in the nucleus of an atom.
• The sun’s light and heat come from fusion reactions, when hydrogen nuclei join to make a helium nucleus.
• Without nuclear energy from the sun, life would not exist on Earth.