1. 1 Motion – Newton’s Laws 1. Every body continues in its state of rest or uniform motion unless it is acted upon by a net external force. 2. The acceleration of a body is equal to the net force acting on the body divided by the mass of the body. a = F NET / m F NET = ma

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11. 11 Motion – Newton’s Laws Special Case: Friction * Friction resists the motion of an object

12. 12 Motion – Newton’s Laws Special Case: Friction * Friction resists the motion of an object * Frictional force is in the opposite direction of the motion of the object

13. 13 Motion – Newton’s Laws Special Case: Friction * Friction resists the motion of an object * Frictional force is in the opposite direction of the motion of the object * Frictional force is proportional to the weight of the object

14. 14 Motion – Newton’s Laws Special Case: Friction * Friction resists the motion of an object * Frictional force is in the opposite direction of the motion of the object * Frictional force is proportional to the weight of the object F FRICTION α mg F FRICTION = μmg The constant of proportionality μ is called the coefficient of friction

15. 15 Motion – Newton’s Laws Special Case: Friction There are two types of friction: Static Friction – frictional force that holds an object stationary. μ s → Coefficient of Static Friction

16. 16 Motion – Newton’s Laws Special Case: Friction There are two types of friction: Kinetic Friction – frictional force associated with a sliding object. μ k → Coefficient of Kinetic Friction

17. 17 Motion – Newton’s Laws Special Case: Friction There are two types of friction: FACT: It requires more force to set an object into motion than it does to keep an object moving. μ s > μ k

18. 18 Motion – Newton’s Laws Special Case: Friction Example: A force is applied to an object, causing the object to slide on a table (with friction) at a constant velocity. The speed is 2 m/sec. If the force is removed, how far will the block slide before it stops? The coefficient of kinetic friction is 0.8 and g = 10 m/s 2

19. 19 Motion – Newton’s Laws Special Case: Friction Example: A force is applied to an object, causing the object to slide on a table (with friction) at a constant velocity. The speed is 2 m/sec. If the force is removed, how far will the block slide before it stops? The coefficient of kinetic friction is 0.8 and g = 10 m/s 2 F = μ k mg → a = μ k mg/m = μ k g Δv = a t → t = Δv/a d = ½ a t 2 = ½ a (Δv/a) 2 = Δv 2 / 2 μ k g d = (2 m/s) 2 / (2 * 0.8 * 10 m/s 2 ) = 0.25 m

20. 20 Motion – Newton’s Laws Special Case: Pressure P = F/A

21. 21 Motion – Newton’s Laws Special Case: Pressure P = F/A F

22. 22 Motion – Newton’s Laws Special Case: Pressure P = F/A F Area

23. 23 Motion – Newton’s Laws Special Case: Pressure P = F/A F Area MKS: N/m 2 British: psi