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

2. Review for test on Monday
Forces
Definition- any push or pull on an object
Units are NEWTONS
Applied forces: contact forces

3. Frictional forces
The force that resist the movement of one surface over the another
Determined by surface conditions, and the forces pressing the 2 surfaces together
Static friction is greater than sliding friction

4. Equation
Ff = μ Fn

5. Coefficient of friction
No units
Measures the interaction between the two surfaces
.1 nearly smooth
.99 very rough

6. Normal Force The force that ground reacts with
Perpendicular to surface and away from surface
At this point generally = to weight of object pressing down on surface

7. 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)

8. 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

9. To calculate net force Combination of all forces on object
Concentrate on forces in dimension of motion
If forces are in same direction, add them
If forces are in the opposite direction, subtract them

10. 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?

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

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

13. 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

14. 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?

15. 2nd Law problem set up #1 Draw free body diagram
#2 Calculate as many of the forces on the FBD as possible
#3 What are the givens?
#4 what do you want?
#5 what equations will connect the givens to what you want
#6 solve and check

16. 2nd law problems Using Fnet = ma Units for each part are…?
Triangle set-up

17. 2nd law problem
A 200 kg crate is pushed horizontally with a force of 700 N. If the coefficient of friction is 0.2:
Calculate the acceleration
Calculate the net force
If its initial velocity was 3 m/s, how fast is it moving after 15 minutes
How far did it travel in 15 minutes

18. 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?

19. 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)

20. What is the velocity and acceleration value at the following points in time of a heavy object being thrown upwards at 5.0 m/s?
Just when it leaves the hand?
At the apex of its flight?
Just before it is grabbed by the hand?

21. 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

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

23. Metric conversion
0.302 km  _________ mm