1. Test Review Hand in day Work/power
Friday PS 10-19
Test Review
Hand in day
Work/power

2. Hand in
Yellow workbook
Seat-belt position paper

3. Review for test on Monday
Forces
Definition- any push or pull on an object
Units are NEWTONS
Identification
Applied forces
Friction
Gravitational forces
Magnetic, electric forces

4. Forces
Balanced forces = when all the forces acting on an object cancel each other out
Unbalanced forces = when all the forces do not cancel each other out (more force on object in one direction than in others)

5. Net force The combination of all forces on an object
For balanced forces Fnet = 0
At rest or at constant velocity
For unbalanced forces Fnet ≠ 0
acceleration

6. Weight, mass Weight = the force due to gravitational pull on an object
W = mg g = 10 m/s2 on earth
Mass = the amount of matter that makes up an object
Differences? Similarities?

7. Inertia
Is the measure of an objects resistance to change in its motion
Directly related to the amount of mass

8. Newton’s 3 laws
!st
2nd
3rd
When does an object change its motion (accelerate)?

9. Collisions and the laws
Be able to use the laws of motion to explain what happens in different types of collisions
Front crash
Rear crash
At least 2 reasons for head rests
Does the bus and the car exert the same amount of force on each other?
Why are people less injured on the bus?

10. Collisions and the laws
Seat-belt configurations
What is wrong with just lap-belts?
Why are seat-belts flat and wide?
What are uses for EKG’s, MRI’s and Xrays?

11. Free body diagrams
FBD’s purpose: To visually show how the forces are arranged on an object
Components of a free-body diagram
Forces
Object
Direction arrow

12. FBD Where do all but the direction arrow originate in the diagram?
How are the forces of air resistance or friction drawn on FBD?
How is the force of gravity drawn on any FBD?

13. 2nd law problems Using Fnet = ma Units for each part are…?
Triangle set-up

14. Advanced 2nd law problems
#1 Have to use the acceleration equation first then use 2nd law
#2 Have to determine Fnet first, then use 2nd law

15. Example
Nicole slows down in her BMW from 15 m/s to 3 m/s in 42 seconds. What is the mass of her car if the net force on it is 7312 N?

16. Law Universal Gravitation
There is a gravitational attraction between any two items that have mass.
The amount of the force is related to the mass of each object and the distance their centers are apart
More mass, less distance  greater force

17. Free Fall
Any object that moves under the influence of only the force due to gravity
Thrown, Dropped objects
Acceleration = 10 m/s2 or (9.8)

18. Terminal velocity The maximum velocity reached by a dropped object
Occurs when the downward gravitational force is matched by the upward force of air resistance
Air resistance depends on surface area and speed of object

19. Action and reaction forces
Identification in the real world
Equal and opposite
Applied to different objects
May have different effects

20. Momentum A quantity of motion
The value of an objects mass times its velocity
To have momentum the object has to be ___________.

21. Change in momentum
To change an object’s momentum requires a net force being applied
The greater the force and the longer the time applied  the bigger change in momentum
Baseball/softball examples
Fender benders vs totaling the car

22. Momentum change in a accident
The amount of change in momentum is constant
Change can be brought about different ways
More time less force
Less time more force
Seat Belts, crumple zones, air bags, Padded dashboards

23. Conservation of momentum
In a system, momentum can not be created or destroyed, but can be transferred
Momentum is direction oriented
Billiards balls

24. Metric conversion
0.302 km  _________ mm

25. What is the difference between distance and displacement?

26. Homework P
Problems 7-11
Problems 18-20
Problems 32,34,39,40

27. Answers to homework P
7 B D B A

28. 18 Free fall means there is only the force of gravity
Weightlessness = no force of gravity
19 less force of gravity, so acceleration due to gravity is less than 9.8
20 when the upward force of air resistance = force of gravity

29. 32 a kg m/s
32 b kg m/s
32 c 0 kg m/s
32 d 12 kg m/s
34 gravitational force is much less (1/16th)
39 acceleration would be doubled
40 a. Train, b. ball, c. equal, equal but opposite