1. Forces Notes

2. 4 Fundamental Forces Gravity - attraction of objects for each other
Electromagnetic force – friction is an example
Strong nuclear force – holds protons together in atoms’ nuclei
Weak nuclear force – holds electrons near nucleus

3. Field Forces & Contact Forces
Field Forces – no touching required
examples: magnetism, gravity
Contact Forces – touching required
examples: pushing, pulling, sliding

4. Field Forces – MagLev Trains

5. Maglev

6. Types of contact forces
Require objects to touch each other
Types of contact forces
Forces can be defined as a push or pull.
Passing a basketball or kicking a soccer ball are both examples of applying a force to an object.

7. Forces Affect How Objects Move:
Change an object’s shape
Start an object moving
Cause an object to move faster
Cause an object to move slower
Cause an object to stop
Cause an object to change direction
Forces Affect How Objects Move:

8. More on Forces: Forces are measured in Newtons (N)
Forces usually act in pairs.
Forces act in specific directions.
Forces are vectors
Forces are represented using arrows
Forces usually can not be seen. Only their effects can be seen.

9. What happens when a force acts on an object?
Depends on STRENGTH and DIRECTION of the force.
Depends on whether the forces are balanced or unbalanced.
Balanced – no change in motion
Unbalanced – change in direction of greatest force.
Try the following examples….

10. Which direction does the box move? Balanced or unbalanced?
PUSH
PUSH
Remember, larger arrows represent larger force. The box will move in the direction with the most force

11. Which direction is this box moving? Balanced or Unbalanced?
PUSH
PUSH

12. What about this box? Balanced or Unbalanced?
PULL
PUSH

13. What direction does this box move? Balanced or Unbalanced?
PUSH
PUSH

14. What direction does the ball roll? Balanced or Unbalanced?
PUSH
PULL

15. The magnitude of the force is measured in Newtons (N)
The magnitude of the force is measured in Newtons (N). This can help in measuring the strength of the force …. Newtons (N)! Unit of measurement for Force!!

16. Which direction is the ball rolling
Which direction is the ball rolling. What is the Magnitude of this force?
PUSH
PUSH
4 N
1 N

17. What is the direction and magnitude of the force causing the face to move?
PULL
PUSH 5N 1N

18. NET FORCE NET FORCES TWO FORCES COMBINE
When two or more forces act on an object at the same time. The forces combine to form a NET FORCE 4N 1N 3N
NET FORCE
TWO FORCES COMBINE

19. CAN COMBINE IN OPPOSITE DIRECTIONS

20. BALANCED FORCES
BALANCED FORCES OCCUR WHEN THE NET FORCE EQUALS ZERO
PUSH
PUSH 3N 3N

21. Opposing forces in action

22. Newton’s Laws of Motion
First Law:
“An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force.”
An object at rest tends to stay at rest. An object in motion tends to stay in motion unless acted on by a net force

23. The First Law and Inertia
Inertia – the tendency of an object to resist a change in motion unless an outside force acts on the object. Example: Riding in a car, driver slams on the brake, purse on the seat slides to the floor.

24. Newton’s Second Law
“The unbalanced force acting on an object equals the object’s mass times its acceleration.”
The unbalanced force on an object determines how much an object speeds up or slows down.
Force = mass x acceleration f=ma

25. F=ma in action

26. So...
For equal forces, a larger mass accelerates less. The yellow ball went farther and faster than the red one.
It’s easier to push a Smart Car than an Escalade.

27. Force is measured in Newtons
One Newton = the force that gives the mass of 1 kg an acceleration of 1 m / s / s
1 N = 1 kg x 1 m/s/s
1 N = lb
1 lb = 4.45 N

28. Force Problems Force = Mass x Acceleration Mass = Force Acceleration
Acceleration = Force Mass
UNITS: mass = kg acceleration = m/s²
force = Newtons

29. Or instead of learning all three types of problems… just do a triangle!

30. Now Try Practice Problems