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.

Adding force vectors

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

Weight, normal force and a box

Unwanted weight loss(descending)

Pulling a box Note: FN is less than mg

Box sliding down

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

Getting the car out of the mud

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

Problem

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

Problem

A double Atwood machine a1= ar- a3 a1= ar- a3