Chapter 9 Section 3 Notes What is Energy?

Energy and Work When energy is done, it is transformed or transferred to another system. Energy can be defined as: the ability to do work Energy can be present in an object even when it is sitting still In order to see that energy, the work must be either transformed or transferred to another system. SI unit for energy is: Joules

Potential Energy PE is called energy of position; it is stored energy Elastic Potential Energy: the energy stored in any type of stretched or compressed elastic material.

Gravitational Potential Energy Gravitational Potential Energy: energy stored in objects separated by a distance; results because of gravitational attraction between objects. Depends on 2 factors: mass height

Gravitational Potential Energy Gravitational Potential Energy Equation: PE = mgh grav. PE = mass x free fall acceleration x height

Potential Energy

Potential Energy This is an example of Potential Energy: the ball is not moving but is has the potential to

Potential Energy

Kinetic Energy KE is the energy of moving objects due to their motion Depends on 2 factors: mass speed

Kinetic Energy Kinetic Energy Equation: KE = ½ mv2 KE = ½ x mass x speed squared

Kinetic Energy Scientific proof for why car crashes are more dangerous at high speeds: KE depends on speed more than mass because speed is squared; so increase in speed = large increase in KE SI unit for KE: Joules

Why Physics is Important! Someone failed their high school physics, loading the cart so much that it tipped backwards. Poor Donkey!

Other Forms of Energy Mechanical energy: the sum of PE and KE in a system

Nonmechanical energy Nonmechanical energy: energy that lies at the level of atoms and doesn’t affect motion on a large scale. Atoms and molecules have KE. Why? Because atoms and molecules are constantly in motion, and KE is energy of motion. KE increases as objects get hotter and decreases as objects get cooler.

Chemical Reactions Chemical reactions involve PE. Why? Since PE depends on position, it is a type of PE. Chemical Energy: energy stored within atoms and molecules that can be released when a substance reacts. If a reaction releases energy, there is a decrease in PE.

Energy Plants get their energy from the sun, and are then able to go through photosynthesis to turn the energy into chemical energy.

Energy How does the sun get its energy? From nuclear fusion; (fusion is the process in which light nuclei join to form heavy nuclei with a large energy release).

Energy Electricity: a form of energy that results from the flow of charged particles through wires. What causes lightning? Electrons traveling through the air between the ground and a thundercloud.

Energy Light can carry energy across empty space: light from sun to earth travels in the form of electromagnetic waves.