1. Forces

2. Objective:
TSW – Identify and describe the changes in position, direction, and speed of an object when acted upon by unbalanced forces.

3. How do forces work?
You’d be surprised at how closely these two concepts go together.
Suppose I asked you to move a heavy desk in the classroom. How would you move it?
Get on one side & start pushing
Grab the legs & start pulling
Either way, you would be using force.

4. Able to change the motion of an object
What is a force?
A force is a push or pull
Able to change the motion of an object
Gravity, friction, and air resistance are three common forces on Earth
Force Video

5. Forces There are many different forces which act on objects.
If forces are balanced the object doesn’t move
If forces are unbalanced the object will do one of the following things:
Begin to move
Stop moving
Change direction
Speed up
Slow down

6. Balanced and Unbalanced Forces
Forces occur in pairs and they can be either balanced or unbalanced

7. Force Diagrams
We can show the forces acting on an object in a force diagram.
In a force diagram, the force is shown with an arrow – the larger the arrow, the bigger the force
The arrows in a force diagram also show the direction that the force is acting on
Sometimes, the arrow will be labeled with the size of the force in Newtons (N)

8. Force Diagrams

9. Balanced Forces
When two forces acting on an object are equal in size, but are opposite in direction, we say the forces are balanced.
Balanced forces do not cause a change in motion.

10. Examples of Balances forces
Forces are balanced when the net force = 0 Newtons
A cell phone resting on the counter
Tying an arm wrestling match
A picture hanging on the wall
Any object with no motion
Any object moving at a constant speed

11. Because Gravity and Upthrust are equal the ship stays afloat.
Balanced Forces
The ship is floating on the water, the forces are balanced. Which forces are acting on the ship?
Because Gravity and Upthrust are equal the ship stays afloat.
(Water’s) Upthrust
Gravity

12. Balanced Forces
The vase is resting on the table. It is not moving, therefore the forces must be balanced.
Which forces are acting on the vase?
Have a look around the classroom and name some of the balanced forces in action on different objects.
Gravity
Table’s Upthrust

13. Unbalanced Forces
Unbalanced forces cause a change in motion by changing the object’s speed or direction.
When two forces are acting on an object and are not equal in size, we say the forces are unbalanced.

14. Unbalanced Forces
Air resistance is pushing upwards
The man and the parachute are slowly falling to the ground.
Which forces are acting on the parachute?
Which force is bigger? How can you tell?
Gravity is the bigger force. We can tell this because the direction of movement of the man and the parachute is the same as the direction of the force of gravity.
Gravity is pulling the man to the ground

15. Examples of Unbalanced Forces
Forces are unbalanced when the net force does not equal 0 Newtons
A football player tackling a quarterback
Pushing a lawnmower across the yard
A skydiver falling toward the ground
Any object that is speeding up, slowing down, or changing direction (accelerating)

16. Gravity is pulling to the ground
Unbalanced Forces
Air resistance is pushing upwards
The same forces are acting on the elephant, but without a parachute there is much less air resistance.
Gravity is a much bigger force. Because there is a bigger difference between the force pulling downwards and the force pushing upwards, the elephant falls much more quickly than a man with a parachute.
Gravity is pulling to the ground

17. Unbalanced Forces The paperclip is jumping up to the magnet.
Which forces are acting on the magnet? Which is the greater force?
The magnetic force is pulling the paperclip upwards
The magnetic force is greater than the force of gravity therefore the paperclip moves in the direction of the biggest force.
Gravity is pulling the paperclip to the ground

18. Forces
Each team is exerting a force – what happens if the pulling force produced by each team is equal?
What would happen if the team on the left were able to produce a bigger pulling force than the team on the right?

19. Unbalanced Forces Based on the forces shown:
Which arm wrestler will likely win?
Which direction will both arms move?

20. Which direction will the rope move?
Unbalanced Forces
4 N, left
10 N, right
Which direction will the rope move?

21. Which direction will the ball roll?
Unbalanced Forces
Which direction will the ball roll?

22. Use the textbook to define the following on your foldable
Force
Balanced Force
Unbalanced Force
Net Force
Newton’s
Mass
Gravity
Weight

23. Interactive Notebook Pages
Use your notes to complete the Venn Diagram on balanced and unbalanced forces.
Then create your balanced and unbalanced forces pockets and sort the images.

24. Net Force
The overall force exerted on an object; measured in Newtons (N)
If the net force is 0, then a change in motion will not occur
If the net force is greater than 0, then a change in motion will occur
5 N + 7 N = 12 N
Net Force

25. How to calculate net force from a picture or diagram
Net Forces
Net Forces
How to calculate net force from a picture or diagram
Subtract the forces if the arrows are pointed toward each other or pointed away from each other
Add the forces together if the arrows are all pointed the same direction OR OR
Practice problem(s) on checkpoint at the end.

26. Practice Problems 5 checkpoint questions
Discuss each question with a partner
Write a complete answer to each question on your notes page

27. Calculate the net force exerted on the box.
Which direction will the box move?

28. Balanced or Unbalanced Forces?

29. Which direction will the airplane move?

30. Why would an object moving at a constant speed experience balanced forces?

31. Identify one example of balanced and unbalanced forces in the room.