Kinetic Energy of Motion Kinetic Energy 2 KE

Kinetic Energy of Motion

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

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

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

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

• kg x m = s x s 2 lkg • m = Joules 2 s

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)(4 kg)(2 m/s) • 8 joules

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

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

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