Energy The ability to do work. An object has energy if it is able to produce change in itself or its surroundings.

Energy exists in different forms Mechanical energy (moving objects and their positions) Radiant energy (light and solar energy) Chemical energy (including the food you eat and fuels we burn) Thermal or heat energy (molecules moving faster means more heat) Electrical energy (electrons moving through a wire) Nuclear energy (energy locked in the nucleus of an atom)

Energy can be transferred… Fossil fuels like coal and oil can be burned to heat water that boils into steam that turns a turbine to generate electricity that you use to operate a stereo. Chemical energy  Thermal energy Thermal energy  Kinetic energy Kinetic energy  Electrical energy

Energy cannot be created or destroyed. In the example of riding a bicycle down a steep hill, you begin with a lot of potential energy at the top of the hill and gain kinetic energy as you coast down the hill. If you are not making the kinetic energy (movement down the hill), where does it come from? The answer is simple: your potential energy at the top is transformed into kinetic energy as you speed along.

Mechanical Energy Kinetic & Potential Kinetic is the energy of moving objects. Potential Energy is stored energy. Gravitational PE is energy due to position.

Potential Energy Energy that is a result of an object’s position or condition. All potential energy is Stored Energy. Pull back on a bow string and bend the bow. The object then possesses potential energy.

Potential Energy A rock on a table top has more potential energy than when it is on the ground due to its position. This is a form of gravitational potential energy.

Gravitational Potential Energy Depends on mass and height. GPE = m(g)h m = mass g = acceleration due to gravity h = height -What are the Units of GPE? Joules

SI units? m = kg g = m/s2 h = m PE = J

Question #1 A man lifts a 2 kilogram book from the floor to the top of a 1.25 meter tall table. What is the change in the book’s gravitational potential energy? 0 joules +2.50 joules -2.50 joules +24.525 joules -24.525 joules

Answer #6: (d) +24.525 J A man lifts a 2 kilogram book from the floor to the top of a 1.25 meter tall table. What is the change in the book’s gravitational potential energy?

Question #2 A mouse now pushes a book (2 kg) off the table (1.25m). What is the change in the book’s gravitational potential energy? 0 joules +2.50 joules -2.50 joules +24.525 joules -24.525 joules

Answer #7: (e) -24.525 J A man lifts a 2 kilogram book from the floor to the top of a 1.25 meter tall table. What is the change in the book’s gravitational potential energy?

Kinetic Energy Energy that appears in the form of motion. Depends on the mass and speed of the object in motion.

Kinetic Energy KE = (1/2)mv2 m = mass v = velocity Unit for energy is Joule (J)

Kinetic Energy Energy due to motion. A brick falling at the same speed as a ping pong ball will do more damage. KE is dependent on mass. KE also depends on speed (v)

Kinetic Energy Which would affect the kinetic energy of an object more, doubling its mass or its velocity? doubling the mass would result in a doubling of the KE. doubling the velocity would quadruple the KE.

Question #8 What is the KE of a 1140 kg (2513 lb) car driving at 8.95 m/s (20 mph)? 0 joules 5101.5 joules 10203 joules 4.57x104 joules I’m lost…

Answer #8: (d) 45658.4 J What is the KE of a 1140 kg (2513 lb) car driving at 8.95 m/s (20 mph)?

Recall, Law of Conservation of Energy Energy can not be created nor destroyed. Energy can change from one form to another. The total energy in the universe is constant.

Conservation of Energy In a roller coaster all of the energy for the entire ride comes from the conveyor belt that takes the cars up the first hill.