1. Chapter 6 and 7

2. momentum = mass x velocity p = mv units: kgm/s or Ns

3. What is the value of the momentum of a 10 kg ball rolling down a bowling alley at a speed of 5 m/s? p = mv p = (10 kg)(5 m/s) p = 50 kgm/s

4. Momentum is a vector, it has a direction The ball bounces off the wall. What is the change in momentum?  p = p final - p initial = 2p

5. Newton’s 2 nd Law: F = ma = m  v/  t p Impulse-Momentum Theorem F  t = p

6. If this girl throws a 0.2 kg snowball at 20 m/s…at you, and it impacts your skull for 0.05 s, what is the force of the impact? F  t = m  vF = m  v/  t F = (0.2 kg)(20 m/s)/0.05 s F = 80 N

7. Stopping Distance A 2500 kg car brakes to slow from 25 m/s to 10 m/s in 6 s. What was the force of braking? F = m  v/  t = (2500 kg)(10 m/s – 25m/s)/6s F = -6250 N How far will it go in that time?  x = ½(v i + v f )  t = ½(25m/s + 10m/s) 6s  x = 105 m

8. Conservation of Momentum The total momentum before equals the total momentum after, if there are no external forces. m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f

9. 80 kg Schoettle steps out of his 100 kg boat with a velocity of 2 m/s. What is the boat’s velocity? m 1 v 1i + m 2 v 2i = m 1 v 1f + m 2 v 2f 0 0 v 2f = -m 1 v 1f /m 2 v 2f = -(80 kg)(2 m/s)/100 kg v 2f = 1.6 m/s

10. Types of collisions (two things hitting each other) Perfectly Inelastic: the two things stick together m 1 v 1i + m 2 v 2i = (m 1 + m 2 )v f 10 kg 5 kg v 1i = 3 m/s What is the velocity after they stick? m 1 v 1i + m 2 v 2i = (m 1 + m 2 )v f m 1 v 1i = (m 1 + m 2 )v f v f = 2 m/s

11. Centripetal Acceleration An object moving in a circle is accelerated toward the center

12. Forces that maintain circular motion Something moving in a circular path has a tendency to want to continue in a tangent path. A force must hold it in its circular path. This is called Centripetal Force. What provides the centripetal force in the picture? What keeps a car on a circular path moving in a circle?

13. Universal Gravitation All matter creates a force of gravity with other matter Force of Gravity Mass of two objects Distance between two objects

14. If I double m 1, what happens to the force of gravity? If I triple m 2, what happens to the force of gravity? If I double the distance between the masses, what happens to the force of gravity? If I halve the distance between the masses, what happens to the force of gravity? If I triple the distance, what happens to the force?

15. F g = mg

16. Rotation: the spinning of an object Revolution: the orbital motion