1. Force and Motion
Unit 4

2. Review Momentum Momentum = How hard it is to stop an object
Formula: P=MV
The object HAS to be in motion in order to have momentum

3. Review Momentum Example: Which of these two has more momentum? Why?
A 5kg basketball traveling at 2 m/sec down the court
A 100 kg golf cart parked under the shade
Which of these two has more momentum? Why?

4. Review Momentum Example:
A 5kg basketball traveling at 2 m/sec down the court
A 100 kg golf cart parked under the shade
Which of these two has more momentum? Why? The basketball has more momentum because it is IN MOTION!

5. Review Momentum Example: Which has the most momentum? Why?
1 kg golf ball, 5 kg basketball, 10 kg bowling ball
All are accelerating at 20 m/sec
Which has the most momentum? Why?

6. Review Momentum Example:
1 kg golf ball, 5 kg basketball, 10 kg bowling ball
All are accelerating at 20 m/sec
Which has the most momentum? Why? The bowling ball because it has the most MASS.

7. Practice Momentum
Time to practice!
You need a calculator!

8. Our Lab
In the lab we explored the relationship between force, mass, and acceleration.

9. What is the relationship between:
Our Lab
What is the relationship between:
Force and Acceleration
Force and Mass
Mass and Acceleration

10. What is the relationship between:
Our Lab
What is the relationship between:
Force and Acceleration = The more force you use the more acceleration the object will have
Force and Mass
Mass and Acceleration

11. What is the relationship between:
Our Lab
What is the relationship between:
Force and Acceleration
Force and Mass = The more mass an object has the more force you need to exert
Mass and Acceleration

12. What is the relationship between:
Our Lab
What is the relationship between:
Force and Acceleration
Force and Mass
Mass and Acceleration = The more mass, the less acceleration; the less mass the more acceleration

13. What is Force?
A force is a push or pull

14. How are force and momentum related?
Momentum = the amount of motion in a moving object
Force = the action of pulling or pushing an object
Applying force to an object causes the motion of an object to change (momentum)

15. Balanced Forces Two types of forces
When forces are acting at the same time on the object
Forces are equal in size and opposite in direction
The students are pushing on the box with equal force but in opposite directions. The forces are balanced. Net force = zero and the box does not move.

16. Unbalanced Forces Two types of forces
These students are pushing on the box with unequal forces in opposite directions. The forces are unbalanced. The box will move in the direction of the larger force. In this case, the box will move to the right.
Unbalanced Forces
Unequal force in opposite directions

17. Unbalanced Forces Two types of forces
It could also be combined forces moving in the SAME direction
The students are pushing on the box in the same direction. The forces are unbalanced. The box will move in the direction that the students push (to the right).

18. A force is a _______________ When are forces on an object balanced?
Quick review
A force is a _______________
Push or pull
When are forces on an object balanced?
When forces are equal in size and opposite in direction

19. We saw in our lab and in the previous examples NOTICEABLE forces
Sometimes, forces are unable to be seen
I need 2 volunteers and 2 textbooks!
Have them both slide their textbooks across the floor at the same time. Have students discuss why the textbook stopped if no one touched it

20. Why did the book stop moving?
What is the unseen, unbalanced force acting on the textbooks?
FRICTION!
In the absence of friction, the book would continue in motion (until another force stopped it)

21. Force and Mass determine Acceleration
Newton’s 2nd law
Force and Mass determine Acceleration

22. Force and Mass determine Acceleration
Newton’s 2nd law
Force and Mass determine Acceleration
This is represented by the formula
F = ma
Unit of Force is Newtons (N)
Unit of Mass is kilograms (kg)
Unit of Acceleration is m/s2

23. Newton’s 2nd law F M V

24. Newton’s 2nd law
If mass remains constant, and we double force, what happens to acceleration?
Example 1
Mass = 10 kg, Acceleration = 5 m/s2, Force = 5 N
Mass = 10 kg, Acceleration = 10 m/s2, Force = 10 N
Acceleration doubles when force doubles

25. Newton’s 2nd law
If FORCE remains constant, and we double MASS, what happens to acceleration?
Example 1
Mass = 5 kg, Acceleration = 10 m/s2, Force = 20 N
Mass = 10 kg, Acceleration = 5 m/s2, Force = 20N
Acceleration decreases when mass increases

26. Newton’s 2nd law
This law also proves that different MASSES accelerate to the Earth at the SAME RATE, but with different FORCES
Let’s watch

27. Newton’s 2nd law Time to practice!
How much force is needed to accelerate a 1,400 kg car 2 m/s2
1st step: WRITE THE FORMULA!
F = M x A
2nd step: Fill in the GIVEN numbers AND units
F = 1,400 kg x 2 m/s2
3rd step: Solve for the unknown
2,800 N

28. Sample problem – calculating force
Force : F=ma
Mass: m=F/a
Acceleration: a=F/m
Two sumo wrestlers face off. The wrestler on the left has a mass of 130 kg and accelerates at a rate of 1 m/s2. The wrestler on the right has a mass of 30 kg and accelerates at a rate of 32 m/s2. Who will generate more force and push his opponent outside the circle?

29. Sample Problem - Calculating Force
F=ma
F=ma
F = 130 X 1
F = 30 X 32
F = 130 N
F = 960 N
130 N
960 N
m= 130 kg
a= 1 m/s2
m= 30 kg
a= 32 m/s2
Confused? Watch this!

30. Does the sumo scenario contradict our investigative phenomenon?
Newton’s 2nd law
Does the sumo scenario contradict our investigative phenomenon?
is our phenomenon still true?

31. Check Your Understanding
1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object?
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.
3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

32. Check Your Understanding
1. What acceleration will result when a 12 N net force applied to a 3 kg object?
12 N = 3 kg x 4 m/s/s
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.
16 N = 3.2 kg x 5 m/s/s
3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?
66 kg-m/sec/sec or 66 N
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?
 9800 kg-m/sec/sec or 9800 N