Forces

1. Forces Chapter 2 Section 3

2. Forces • Throwing a baseball, serving a volleyball, or just standing up are all examples of forces. • Force is a push or a pull that one body exerts on another. Because of this force, the object moves. • Can you think of any other instances when you exert a force on something?

3. Changing Motion • What happens to the motion of something when you apply a force to it? • The applied force can cause the object to change directions.

4. Changing Motion EXAMPLE • Think of playing volleyball… • The server on the other team serves the ball. The ball is heading toward you. You bump the ball. The ball now heads up, away from you. By bumping the ball, you are applying a force and the ball changes direction.

5. Balanced Forces • Applying a force does not always change the velocity. • Remember velocity = speed +direction

6. Balanced Forces • If I have a chair and I push on one side of it with a force of 25 N and you push on the other side, with a force of 25 N, will the chair move? • NO • Why? 25 N 25 N

7. 25 N 25 N Balanced Forces • The net force is when two or more forces are applied on the same object and at the same time. The applied forces combined are called the net force. = 0

8. Balanced Forces • The force I apply in one direction plus the force you apply in the opposite direction are added together. • 25 N + (-25 N) = 0 • Because the forces are equal and balanced…just like a balanced scale…this is an example of balanced forces.

9. Unbalanced Forces • What does it mean to have something unbalanced? • Unequal, not the same, different • How could we have unbalanced forces?

10. Unbalanced Forces • There are two types…can you guess what they are? • First type = one person applies a force in one direction and the other person applies a smaller force in the opposite direction. • Second type = both people apply a force in the same direction

11. 50 N 25 N Unbalanced Forces First Type: • If I have a chair and I push on one side of it with a force of 50 N and you push on the other side, with a force of 25 N, will the chair move? • YES! • Which way will it move? • In the direction I am pushing it. • Or the direction in which the most force is applied • What is the net force in this example?

12. 50 N = 25 N 25 N Unbalanced Forces • 50 N + (-25N) = 25 N • These forces are unequal so the forces are considered unbalanced forces.

13. Unbalanced Forces Second Type: • If I push the chair in one direction with 25 N force and you push the chair in same direction with 25 N force, will the chair move? • YES • Why? • Because the applied net force is… • UNBALANCED!

14. Unbalanced Forces • The result would be the chair moving in the direction it was pushed with a combined force of 50 N. 25 N = 50 N 25 N

15. INERTIA & MASS Chapter 2 Section 3

16. Inertia & Mass • Inertia is the tendency of an object to resist any change in its motion. • An object will continue to move at the same speed in the same direction unless acted upon by an unbalanced force.

17. Inertia & Mass • If you took a bowling ball and rolled it down the street, what would happen? Why? • Friction is an unbalanced force that causes the ball to stop or slow down. Without friction, the ball would keep going.

18. Inertia & Mass • Does a bowling ball and a tennis ball have the same inertia? … • NO • Why?

19. Inertia & Mass • If you had a tennis racket and I threw a tennis ball at you, what would happen? • If you had a tennis racket and I threw a bowling ball at you, what would happen? • Why could you change the motion of the tennis ball but not the motion of the bowling ball?

20. What is mass? Mass is the amount of matter in an object. A bowling ball has more mass than a tennis ball. The greater the mass of an object the greater its inertia. Inertia & Mass