1. Forces

2. Force A push or a pull that may cause an object’s motion to change!
Unit for force is the Newton(N)!
It is a vector quantity.
Direction is important!!

3. Do forces have to be “in contact” in order to have an affect on another object?

4. Balanced vs. Unbalanced Forces”
Balanced forces—forces that are equal in magnitude, but opposite in direction!!
Will not cause a change in the motion of the object!!
Unbalanced forces—forces that are not equal in magnitude and opposite in direction!
Will cause a change in the motion of the object!!

5. Are the forces Balanced or Unbalanced?

6. Balanced or Unbalanced:

7. Balanced or Unbalanced:

8. Net Force(Fnet) Sum of all forces acting on an object.
If there is a net force acting on an object, the velocity of the object will change!!

9. Balanced or Unbalanced? Find the Net Force
FNet = 30 N left

10. Balanced or Unbalanced? Find the Net Force
FNet = 0 N

11. Balanced or Unbalanced? Find the Net Force
FNet = 10 N Right

12. Balanced or Unbalanced? Find the Net Force
FNet = 130 N down

13. Balanced or Unbalanced? Find the Net Force
FNet = 360 N right

14. Find the Net force in the diagram below:
120 N right
120 N left
20 N right
20 N left

15. Determine the Net Force:
10 N right
150 N right
160 N right
150 N left

17. Newton’s 1st Law of Motion
also known as the “Law of Inertia”.
Inertia—tendency of an object to resist change in motion.
Explain?????
What does inertia depend on?
1st Law--An object at rest stays at rest and an object in motion stays in motion, unless acted on by some unbalanced force!

18. More thoughts on Inertia:
What gives an object inertia????

19. Inertia(cont): Mass gives an object inertia!!
It is easier to change the motion of a small object than it is to change the motion of a larger object!!
Does anything else affect inertia?

20. I must think about balancing my bike!!!
Inertia(cont.)
Think about a bicycle!!
Ever tried to balance on a bike while standing still?
Was it easy?
Was it impossible?

21. I must think about balancing my bike!!!
Inertia(cont.)
I must think about balancing my bike!!!
When you ride your bike down the road, how many of you think to yourself, “I must balance my bike, I must balance my bike!!”
What’s the difference?
Click me #1
Click me #2

22. Newton’s 1st Law of Motion(cont.)
If you roll a ball across the floor, why does it eventually come to a stop.
Is there a force acting against it?
If so, what is it?
Friction—force that opposes motion.
Always acts in the direction opposite of motion.
Anything slowing this Coke as it slides across the bar?

23. Newton’s 2nd Law of Motion
called the “Law of Acceleration”.
Relates force, mass, and acceleration.
Force and acceleration directly related.
Mass and acceleration inversely related.

24. Newton’s 2nd Law of Motion(cont.)
F = m a
Where:
F = force in Newton’s(N)
m = mass in kilograms(kg)
a = acceleration in m/s2

25. Ex. What force is required to accelerate a 1500 kg car by a rate of 1
Ex. What force is required to accelerate a 1500 kg car by a rate of 1.5 m/s/s?
Given:
m = 1500 kg
a = 1.5 m/s/s
F = ?
F = m a
F = 1500kg(1.5 m/s/s)
F = 2250 N

26. Ex. A force of 290 N is applied to a 20 kg rock
Ex. A force of 290 N is applied to a 20 kg rock. At what rate will the rock accelerate?
F = m a
a = 14.5 m/s2
Given:
m = 20 kg
a = ?
F = 290 N

27. Ex. A force of 140 N is applied to a mover’s dolly to accelerate a load of Cokes across the grocery store at 3 m/s2. What is the mass of the load of Cokes?
Given:
F = 140 N
a = 3 m/s2
m = ?

28. A force is applied to accelerate a 50 kg mass at a rate of 2. 5 m/s/s
A force is applied to accelerate a 50 kg mass at a rate of 2.5 m/s/s. What force is required?
20 N
25 N
120 N
125 N

29. 3000 m/s/s 240 m/s/s 20.8 m/s/s .05 m/s/s
A 250 N is applied to a 12 kg mass. At what rate will the object accelerate?
3000 m/s/s
240 m/s/s
20.8 m/s/s
.05 m/s/s

30. Newton’s 3rd Law
For every action, there is an equal but opposite reaction.
Forces always occur in pairs!!

31. Which of the following scenarios does not represent Newton’s 3rd Law?
A rocket being launched into space.
A book resting on a desk.
A person paddling a canoe.
A large force pushing on a small mass, causing it to accelerate.