1. SECOND QUARTER! Its second quarter time!
Lets continue on with Forces, but first

2. EXAMS (seats next class)
Your exams (look at, not keep yet)

3. AN EXAMPLE
A 500kg rocket is going up at 5m/s2. How much force is the engine pushing it up.
Explain why doing F = ma to get (500)(5) = 2500N is WRONG

4. AN EXAMPLE
A 500kg rocket is going up at 5m/s2. How much force is the engine pushing it up.

6. And it depends if you go DOWN or UP….
ELEVATORS
In an elevator, you feel lighter/heavier in your knees at the start/end of the elevator ride.
And it depends if you go DOWN or UP….

7. The FORCE we feel is the ground pushing up….the normal force.
That’s why we can feel weightless as we fall even though our weight does not change.

8. Elevator going UP at a constant velocity:
LETS TRY
Elevator going UP at a constant velocity:

9. Elevator going UP and speeding up
Predict: Which way is the imbalance? So which is larger?
Predict the net force equation

10. Elevator going UP and slowing down
Predict: Which way is the imbalance? So which is larger?
Predict the net force equation

11. Elevator going UP and slowing down
LETS TRY
Elevator going UP and slowing down

12. Elevator going DOWN at constant velocity
LETS TRY
Elevator going DOWN at constant velocity

13. Elevator going DOWN and speeding up
Predict: Which way is the imbalance? So which is larger?
Predict the net force equation

14. Elevator going DOWN and speeding up
LETS TRY
Elevator going DOWN and speeding up

15. Elevator going DOWN and slowing down
LETS TRY
Elevator going DOWN and slowing down

16. 6) An elevator lifts a panda up at an upwards acceleration of a.
a) Which is larger then, the up force of the elevator cable or the weight?

17. 6) An elevator lifts a panda up at an upwards acceleration of a.
c) Draw a FBD of the panda, call the elevator force the normal force, the panda's mass M.

18. 6) An elevator lifts a panda up at an upwards acceleration of a.
d) Create a net force equation for the panda's situation.
e) If the elevator had 600N of force up, how much mass was the panda?

19. The Example I do
A force of 20N is needed to overcome the frictional force of 5N and accelerate a 3kg mass across the floor. What is its acceleration?

20. YOU TRY…
A 10kg mass is moving to the right at 6m/s, and you are pulling it right with a force of 20N. Friction is present.
A) If you want the mass to come to a stop in 12 seconds, what acceleration would it have?

21. YOU TRY…
A 10kg mass is moving to the right at 6m/s, and you are pulling it right with a force of 20N. Friction is present.
B) How much friction is required to stop it after 12 seconds even though you are pulling it.

22. YOU TRY…
A 10kg mass is moving to the right at 6m/s, and you are pulling it right with a force of 20N. Friction is present.
Find the coefficient of friction:

24. LETS TRY A HW Q: NUMBER 3
Start with the first one; creating FBD’s