What is energy? ENERGY is the ability to make things move or change Measured in Joules (J) = Nm

Forms of energy Energy can exist in many different forms and changes from one form to another

Kinetic Energy KINETIC ENERGY is the energy of motion Depends on mass and velocity

Kinetic Energy Formula: KE = ½mv2 mass (in kg) velocity (in m/s)

Work it Out with a Partner! A baseball has a mass of about 0.15 kg. A pitcher throws the ball at 40 m/s (this is about 90 mph). How much kinetic energy does the ball have?

Potential Energy An object with POTENTIAL ENERGY has the ability (or potential) to move or change Sometimes called “energy of position” or “stored energy” There are 3 types of potential energy: Gravitational Potential Energy Elastic Potential Energy Chemical Potential Energy

Gravitational Potential Energy Potential Energy due to an object’s position Formula: PE = mgh height (in meters) mass (in kg) acceleration of gravity (9.8 m/s2)

Gravitational Potential Energy The person has more potential energy at the top of the stairs than at the bottom.

Gravitational Potential Energy Where does the egg have more potential energy? Why?

Work it Out with a Partner A cat is on the top branch of a tree. The tree is 15 meters high and the cat has a mass of 5 kg. How much potential energy does the cat have?

Elastic Potential Energy Potential energy due compression or expansion of an elastic object

Chemical Potential Energy Potential energy stored within the chemical bonds of an object

Practice Problems 1. 0.20 kg apple hangs on a tree and has 14 J of potential energy. How high off the ground is the apple? 2. A student eats a candy bar that can provide 1.57 x 106J of energy. If the student has a mass of 81.8 kg, how high will he have to climb a ladder to offset completely the energy contained in the candy bar? 3. The diagram below represents a 155 N box on a ramp. A force is applied that will cause the box to slide from point A to point B. What is the total amount of gravitational potential energy gained by the box? 7.14 m 1958 m 278.7 m

The Law of Conservation of Energy Energy cannot be created or destroyed; it can only be transformed from one form to another Mechanical energy = KE + PE Mechanical energy is always constant!

What happens when the cord is cut? Potential energy is converted to kinetic energy!

Mechanical Energy always = 100 J  Energy is Conserved PE = 100 J KE = 0 J PE = 100 J KE = 0 J PE = 50 J KE = 50 J PE = 50 J KE = 50 J PE = 0 J KE = 100 J

Rollercoaster Have you ever been on a roller coaster that went higher on the second hill than on the first? It’s physically impossible! The roller coaster can never have more potential energy than it started with at the beginning.

Kinetic and potential energy convert to one another

Now what would happen if the loops were as high as the starting point? Max P No K Max P No K Max P No K Max P No K No P Max K No P Max K

Do the problems on the online ws I have posted an answer key. Please use it to help you figure out how to solve the problems.