1. Unit 4 Motion & Forces

2. 3. Balanced and Unbalanced Forces

3. Suppose you are asked to move a heavy desk in your classroom.
How would you move it?

4. You might get on one side of the desk and start pushing
Or you might grab the legs and start pulling

5. Either way, you would be using a force
Vocabulary:
force
any push or pull

6. The force you use in pushing or pulling the desk has a size
F = 1200 N F = 50 N F = 600 N
F = 50 N
You could use a small amount of force or a lot of force
Forces differ in size

7. Another way forces differ is in direction
A force can be left or right,
Up or down

8. The desk will not move by itself
Force
Force
A force is needed to put the desk in motion

9. But even when the desk is not moving
Forces are acting upon it

10. The floor is actually pushing up on the desk

11. The force of gravity is pulling down on it
At the same time
Gravity
Floor
The force of gravity is pulling down on it

12. If the object is not in motion
The upward force is the same as the downward pull

13. The size of the forces is the same
But the directions of the forces are different

14. Whenever forces are the same in size but opposite in direction
They are balanced forces

15. An object that is not in motion will never move if balanced forces act on it

16. How can you move the object?
You can move it because you unbalance the forces

17. The size of your force is greater than the force of air pushing on the other side of the teeter totter

18. Unbalanced forces act in opposite directions but differ in size

19. If unbalanced forces act on an object
The object will always move in the direction of the greater force