FORCES AND LAWS OF MOTION

1. FORCES AND LAWS OF MOTION

2. FORCE (push) (pull)

4. Examples of forces:

5. Free body diagram

6. Free body diagram

7. A free-body-diagram is a diagram that represents the object and the forces that act on it.

8. The net force on an object is the vector sum of all forces acting on that object. The SI unit of force is the Newton (N). Individual Forces Net Force 4 N 10 N 6 N

9. Net Force

10. Individual Forces Net Force 5 N 3 N 4 N

12. 1) A hockey puck is sliding on a frictionless ice.2) A hockey puck is sliding on a normal ice (with friction)

13. FBD - Practice Many orangutans spend their entire lives among the trees and are well adapted to move in this arboreal habitat. They have long arms (about two-thirds of their body height) and powerful chest muscles. Suppose an adult orangutan is hanging by its arms from a tree branch. The angle between each of the animal’s arms and the vertical is 15° with each arm exerting a force 430 N. The gravitational force acting on it is 830 N. Draw a free-body diagram of the animal.

14. FBD - Practice Rock wall climbing is a challenging activity. Suppose that on one ascent, a climbing piton is wedged into a crevice on the rock wall. A climber negotiating the wall exerts a force of 350 N at an angle of 65° below the horizontal on a rope secured to the piton. The rock surrounding the piton exerts an upward force of 320 N and a horizontal force of 150 N to the left on the pin. Draw a free-body diagram of the pin.

15. FBD - Practice After a skydiver jumps from a plane, the only force initially acting onthe diver is Earth’s gravitational attraction. After about ten seconds of falling, air resistance on the diver will have increased so that its magnitude on the diver is now equal in magnitude to Earth’s gravitational force on the diver. At this time, a diver in a belly-down position will be falling at a constant speed of about 190 km/h. a. Draw a free-body diagram of the skydiver when the diver initially leaves the plane. b. Draw a free-body diagram of the skydiver at the tenth second of the falling.

16. FBD - Practice A chef places an open sack of flour on a kitchen scale. The scale reading of 40 N indicates that the scale is exerting an upward force of 40 N on the sack. The magnitude of this force equals the magnitude of the force of Earth’s gravitational attraction on the sack. The chef then exerts an upward force of 10 N on the bag and the scale reading falls to 30 N. Draw a free-body diagram of the latter situation.

17. FBD - Practice A music box within the toy shown below plays tunes when the toy is pushed along the floor. As a child pushes along the handlebars witha force of 5 N, the floor exerts a force of 13 N directly upward on the toy. The Earth’s gravitational force on the toy is 10 N downward while inter- actions between the wheels and the floor produce a backward force of2 N on the toy as it moves. Draw a free-body diagram of the toy as it is being pushed.

18. Aristotle 384 – 322 BC

19. 1564 - 1642

20. 1643 - 1727 ISAAC NEWTON