1. Ch 4. Forces & Newton’s Laws of Motion
Individual
Net
5 N
force = a push or a pull.
3 N
Unit of Force = Newton
net force = vector sum of all forces on object
4 N
net force =
Individual Forces
Newton’s 1st Law:
object – stays at rest – or constant speed in a straight line – if no net force.
4 N
10 N
Net Force
Inertia = tendency of object
to stay at rest – or constant speed in a straight line – if no net force.
6 N

2. Mass (m) is the amount of “stuff” in an object free-body-diagram
represents object & forces
Unit of Mass: kilogram (kg)
Newton’s 2nd Law:
Acceleration – proportional to Force – inversely proportional to mass
Net force:
275 N N – 560 N = +110 N
along the + x axis
Units
Acceleration: mass of car = 1850kg
Unit of Force = Newton

3. Net force: +17 N Force x component y component +(15 N) cos67 0 N
+(15 N) sin67
+23 N
+14 N
forces

4. Newton’s 3rd Law: Action = Reaction Force from body-A to body-B =
Force from body-B to body-A
Magnitude of force is 36 N. Mass of spacecraft is 11,000 kg. Mass of astronaut is 92 kg.
What are the accelerations?

5. Newton’s Law of Gravitation Weight
= gravitational force earth attracts object
masses m1 and m2 separated by
distance r, gravitational force 
12 kg
25 kg
1.2 m
On earth’s surface

6. = normal force on scale by man
from surface
to object
Apparent Weight
= normal force on scale by man
true
weight
apparent
weight

7. coefficient of static friction.
Frictional Force
static friction
coefficient of static friction.
After motion begins
coefficient of kinetic friction = 0.05
mass = 40kg
What is the kinetic frictional force?
coefficient of kinetic friction

8. Equilibrium Tension Force Equilibrium
Cables and ropes transmit forces through tension.
Equilibrium
Reasoning Strategy
select an object in equilibrium
draw free-body diagram for object & forces
choose x,y axes
resolve forces into x,y comps
apply equilibrium equations
solve for unknown quantities

9. Equilibrium
Force
x component
y component

10. Non-Equilibrium When an object is accelerating,
it is not in equilibrium.
you are given m,a,R,D