1. Kinetic Energy Energy of Motion

2. Kinetic Energy KE = ½ mv 2 m = mass v = speed (velocity) KE = ½ mv 2 m = mass v = speed (velocity)

3. AAK! A Formula! The letters are variables and they’re placeholders for actual numbers. Because the letters are side- by-side, you multiply them together. To figure out kinetic energy, put numbers for both and multiply together. The letters are variables and they’re placeholders for actual numbers. Because the letters are side- by-side, you multiply them together. To figure out kinetic energy, put numbers for both and multiply together.

4. But what about v 2 ? That just means you take the number for v and multiply it by itself. For example, if v = 3, then v 2 = 3x3 3x3 = 9 That just means you take the number for v and multiply it by itself. For example, if v = 3, then v 2 = 3x3 3x3 = 9

5. What units do I use? Mass is measured in… Kilograms Speed is measured in… Meters/Second If you square speed, you get… Meters 2 /Second 2 Mass is measured in… Kilograms Speed is measured in… Meters/Second If you square speed, you get… Meters 2 /Second 2

6. kg x m x m = s x s kg x m x m = s x s kgm 2 = Joules s 2

7. Let’s Try Some Equations KE = 1/2 mv 2 For example, plug in 4 kilograms for m and 2 m/s in for speed. What’s the kinetic energy? (1/2)(4kg)(2 m/s)(2 m/s) 8 joules KE = 1/2 mv 2 For example, plug in 4 kilograms for m and 2 m/s in for speed. What’s the kinetic energy? (1/2)(4kg)(2 m/s)(2 m/s) 8 joules

8. What if you double the mass? Ex 1: mass = 4 kg, speed = 2 m/s KE = 1/2 (4kg)(2 m/s)(2 m/s) KE = 8 Joules Ex 2: mass = 8 kg, speed = 2 m/s KE = 1/2 (8kg)(2 m/s)(2 m/s) KE = 16 Joules So, if you double the mass, you double the energy--how were our results? Ex 1: mass = 4 kg, speed = 2 m/s KE = 1/2 (4kg)(2 m/s)(2 m/s) KE = 8 Joules Ex 2: mass = 8 kg, speed = 2 m/s KE = 1/2 (8kg)(2 m/s)(2 m/s) KE = 16 Joules So, if you double the mass, you double the energy--how were our results?

9. What if you double the speed? Ex 1: mass = 4 kg, speed = 2 m/s KE = 1/2 (4kg)(2 m/s)(2 m/s) KE = 8 Joules Ex 2: mass = 4 kg, speed = 4 m/s KE = 1/2 (4kg)(4 m/s)(4 m/s) KE = 32 Joules So, if you double the speed, you QUADRUPLE the energy--how were our results? Ex 1: mass = 4 kg, speed = 2 m/s KE = 1/2 (4kg)(2 m/s)(2 m/s) KE = 8 Joules Ex 2: mass = 4 kg, speed = 4 m/s KE = 1/2 (4kg)(4 m/s)(4 m/s) KE = 32 Joules So, if you double the speed, you QUADRUPLE the energy--how were our results?

10. Learning Check! Car crash tests have cars smashing into walls traveling at about 50 km/hr. This is about equal to 15 m/s. An average car has a mass of about 1000 kg. How much kinetic energy does the car have right before it hits the wall? KE = 1/2 mv 2 KE = 1/2 (1000 kg)(15 m/s) 2 KE = 112500 Joules Car crash tests have cars smashing into walls traveling at about 50 km/hr. This is about equal to 15 m/s. An average car has a mass of about 1000 kg. How much kinetic energy does the car have right before it hits the wall? KE = 1/2 mv 2 KE = 1/2 (1000 kg)(15 m/s) 2 KE = 112500 Joules