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Kinetic Energy

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

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Kinetic Energy

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  1. Kinetic Energy Energy of Motion

  2. Kinetic Energy • KE = ½ mv2 • 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.

  4. But what about v2? • That just means you take the number for v and multiply it by itself. • For example, if v = 3, then v2 = 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… • Meters2/Second2

  6. kg x m x m= s x s • kg•m2= Joules s2

  7. Let’s Try Some Equations • KE = 1/2 mv2 • 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?

  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?

  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 mv2 • KE = 1/2 (1000 kg)(15 m/s)2 • KE = 112500 Joules

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