CBA Warm up

1. CBA Warm up A cup slides off the table with an unknown velocity. The table is 1 m high and the cup hits the ground 2.5 m from the edge of the table. What was the velocity of the cup as it flew off the table?

2. CBA Warm up A young kid pushes a cup with a mass 0.25 kg off the table; it slides off the table with an unknown velocity. The table is 1 m high and the cup hits the ground 2.5 m from the edge of the table. What was the force applied to the cup by the kid as it flew off the table if he pushed it for 0.5s and the cup was sitting still on the table when he started pushing it?

3. Physics HonorsA/B –Day 10/27-10/28/14 Free body Diagrams and Frictional Forces

4. Test

5. Agenda • Announcement: Retest - • Friction • Static • Kinetic • Free Body Diagrams

6. Why do we care about friction in real world? When do we use friction? • Walking, driving, writing When would we want to reduce friction? • In moving mechanical part – like engine of car – causes wear • Wastes energy New Technology in reducing friction • Liquid Crystal Lubricants, (same crystals that are in LCD screens)

7. What happens when we push something • We lightly apply a force. This force applied is canceled out by the frictional force.

8. What happens when we push something • We lightly apply a force. This force applied is canceled out by the frictional force.

9. What happens when we push something • We lightly apply a force. This force applied is canceled out by the frictional force.

10. What happens when we push something • Until we hit a point where we overcome friction and we start moving.

11. 2 Regions of friction are being observed • Static Friction – is the resistive force that opposes the relative motion of two contacting surfaces that are at rest with respect to one another The friction that keeps the object from moving is static friction.

12. 2 Regions of friction are being observed • Once the object starts moving new type of friction • Kinetic Friction – the resistive force that opposes the relative motion of two contacting surfaces that are moving past one another The friction that slows down the object moving is kinetic friction.

13. 2 Regions of friction are being observed

14. What causes Friction • Static friction arises from • microscopic roughness of the two surfaces • Electrostatic forces • Atomic Forces • Van der Waal Forces (in non metals) • Metallic bonding (in metals)

15. What causes Friction

16. The surfaces determine the coefficients of static or kinetic friction • So this leads to the fact that different materials will have different coefficients of friction

17. Example Problem • A wooden box is on a wood floor and is trying to be pushed across the room. If the box has a mass of 100 kg, what will be the Force at which the box will start to move?

18. Example Problem • A wooden box is on a wood floor and is pushed across the room. If the box has a mass of 100 kg, what is the Force being exerted on the box if it is accelerating with a rate of 0.7 m/s?

19. Example Problem • A wooden box is on a wood floor and is being pushed across the room. If the box has a mass of 100 kg, what is the Force being exerted on the box if it is moving with a constant velocity?

20. Example Problem • A box is on aincline plane and being held in place by the Force due to Static Friction. Determine the coefficient of static friction between the box and the ramp.

21. Example Problem • A box slides down an incline plane with an acceleration of 1.20 . Determine the coefficient of kinetic friction between the box and the ramp.