Transcript Newton`s Laws Slides

1
Newton’s First Law
Newton’s First Law (cont)
v
v
v
An object at rest tends to remain at rest and an object in motion
tends to remain in motion in a straight line at constant speed,
unless acted upon by an unbalanced (net) force.
This tendency not to change velocity is called
The measure of an object’s inertia is called
v
Net Force
v
F4
F1
F2
F3 = Fg
Examples of Inertia
Newton’s Second Law
Newton’s Second Law (cont)
Fnet
v1
v2
a
v3
Force of Gravity - Weight
Fg
Fs
Force of Gravity (continued)
How is it that a 2 kg mass doesn’t fall with twice the
acceleration of a 1 kg mass? It is twice as massive!
In the absence of air resistance all masses fall with the
same acceleration. How is this possible?
m
2m
Fg
2Fg
F1
F2
Newton’s Third Law
F1 = force of girl on wall
F2 = force of wall on girl
F1 = - F2
F2
F1
Sample Problem 1
A fully clothed boy stands in the middle of a frozen pond. There is 0 friction between the
boy and the surface of the pond. Use Newton’s Laws to explain how the boy can get to the
bank of the pond with no external help (force).
m2
m1
A 100 kg boy and a 50 kg girl stand on a frictionless frozen lake 6.0 m apart. They each hold the end of a
massless rope. The boy pulls on the rope with a force of FG and continues to exert the force until they meet.
The girl holds on to her end of the rope at all times. a) With what force does the girl pull on the boy? b)
What is the acceleration of the girl compared to the boy? c) How far does the boy travel? d) The girl?
mG
mB
FG
6.0 m
Explain the Picture
Explain the Picture (cont)
100N
100N
80N
120N