1. Chapter 4: Dynamics, Newton’s Laws
First Law: Every body stays in its state of motion( rest or uniform speed) unless acted on by a non zero net force.
Second Law: The acceleration is directly proportional to the net force and inversely proportional to the mass:
Third Law: Action is equal to reaction.

4. Adding force vectors

5. pulling a sled, Michelangelo’s assistant
For forward motion: FAG> FAS FSA > FSG

7. Weight, normal force and a box

9. Unwanted weight loss(descending)

11. Pulling a box
Note: FN is less than mg

13. Box sliding down

15. The advantage of a pulley
For moving with constant speed a=0

17. Getting the car out of the mud

19. Atwood’s Machine FT=? a=?
Draw a free body diagram for each mass and choose up positive, then a2= a , a1= -a
FT - m1g = m1a1= -m1a
FT – m2g = m2a2= m2a
(m1–m2)g=(m1+m2)a

20. Problem

23. Q10: Where does the thread break?
Q10: Why does the force need to pull the backpack up increase?

25. Problem

27. A double Atwood machine
a1= ar- a a1= ar- a3