8.6A: Forces
Net Forces: Sum of all forces acting on an
object.
Balanced Forces: When forces on a single object
are equal and the sum is 0N, no change in
movement will occur.
Unbalanced Forces: When forces on a single
object are NOT equal and the sum is greater
than 0, acceleration occurs.
4N
What is the net force acting on the couch?
41N to the Right
8.6B: Speed, Velocity, & Acceleration
Speed: How far an object travels in a given time.
 mph, km/hr, m/s
Velocity: The speed and direction an object
travels.
 mph North
 km/hr Southwest
 m/s East
Acceleration: The change in velocity (change in
speed or direction).
 Acceleration of an object requires an
unbalanced force.
 A merry-go-round, car turning on a race
track, increasing or decreasing speed
 Units include m/s/s or m/s2
The list below includes 6 situations.
Example: a person flies forward in a car when
they hit their breaks. For this reason, people
should always wear seatbelts.
You are waiting at a red light in a vehicle with a
cup of coffee sitting on your dashboard. The car
behind you does not see you and rear-ends
your car.
According to the information above, what
happens to the coffee cup? The cup falls into
your lap because an object at rest wants to stay
at rest. The force exerted on the car moves the
car, but the coffee does not move with the car.
2nd Law of Force and Acceleration: F=MA
If both objects have the same amount of force
exerted, which one will have the most
acceleration? Object A
What is the net force acting on the rope?
20N to the Left
Which situation(s) will experience an
unbalanced force? 1, 3, 4, 6
8.6C: Newton’s Laws of Motion
1st Law of Inertia: Objects at rest stay at rest
and objects in motion stay in motion, unless
acted on by an unbalanced force.
Inertia: an objects resistance to change motion
(more mass = more inertia).
What is the net force acting on the scale?
0N (No Movement)
If both object have the same amount of mass,
which object will have the most acceleration?
Object B
A man hits a 0.2kg golf ball 20m/s2. What force
was acted on the ball? 4N
What is the mass of a falling rock if it produces a
force of 147N? 15kg
Four students raced toy cars on a track. The
mass and the acceleration of each car is
recorded in the table below.
3rd Law of Action/Reaction: For every action,
there is an equal and opposite reaction.
Examples: Rocket launching, bouncing a ball,
jumping, swimming, canoeing
A student jumps off a sled toward the west
after it stops at the bottom of an icy hill.
8.3D: People
Aristotle thought mass influenced the speed of
falling objects. Galileo proved him wrong. All
objects fall with the same acceleration.
Frictional forces between the surface area of
objects and air slows falling objects. In the
absence of air, all objects fall at the same rate;
9.8m/s/s.
8.6B: Acceleration
Gravity has an acceleration of 9.8m/s2 or m/s/s.
In other words, objects fall faster or increase
speed the longer they fall.
Which toy car had the greatest applied force? 4
If an object falls for 20 seconds, what speed will
it have?
196 m/s
The diagram below shows two different forces
acting on a cyclist riding a bicycle.
If the speed of a falling object is 19.6 m/s, how
long did it take to get to that speed?
2 seconds
Based on the law of action–reaction, in what
direction will the sled most likely move as the
student jumps off? West
A squid moves through water by ejecting water
out of its body into the surrounding water.
When the water is pushed out, the ejected
water pushes back and thrusts the squid
forward.
The total mass of the cyclist and the bicycle is
90 kg. Based on this information, what is the
acceleration of the cyclist? 0.77m/s2
Which of Newton’s Laws bests describes this
scenario? 3rd Law of Action/Reaction