Ch.3:1 Name: Period:
Isaac Newton’s 3 Laws of Motion
Sir Isaac Newton (1642-1727) was an English physicist and mathematician. Before the age of 30 he formulated the laws of motion and invented calculus. Much of our modern science is based on Newton’s
Newton’s Laws of Motion
Law One – Law of Inertia
Law Three – An object at rest will stay at rest unless
Law of Equal and Opposite Forces. acted on by an unbalance force.
Whenever one object exerts a force on An object in motion will stay
another object, the second exert an in motion unless acted upon by
equal and opposite force on the first. an unbalanced force.
OR OR Things keep moving or stay at rest, unless a net force acts upon them.
Law Two – F = ma The acceleration of an object is propor- tional to the force acting on it and inversely proportional to its mass.
OR
Force causes acceleration,
For every action there is an equal while mass resists acceleration
and opposite reaction.
Inertia
A force is any action that can change or cause motion. A force is any push or pull. Inertia is the property of
We use Newtons (N) to measure force. an object that resists
change of motion.
Moving objects have inertia: they want to keep moving; stopped objects have inertia: they want to stay at rest.
More mass = more inertia!
Something that is harder to push has more inertia!
Newton’s Second Law
F = ma
Force equals mass times acceleration.
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Force
More mass, more inertia
Net Force Net force is the sum of all the forces and has direction.
(Be sure to make right positive and left negative.)
An object will move in the direction of the net Less mass,
(or unbalanced) less inertia
force.
- 400 N + 200 N
Net Force = + 200 N – 400 N = – 200 N (left)
F = ma tells us:
Force (in Newtons)
Mass (in kg)
For the same acceleration, more mass requires more force. Acceleration (in m/sec2)
For the same mass, more acceleration requires more force.
Ex. How big a force does it take to give a 50 kg object an acceleration of 40 m/s2.
Ex. If a 50 N force pulls on a 10 kg object, how much acceleration will occur? Variables:
Variables: 40 m/s2 = a
50 N = F 50 kg = m
10 kg = m F = ?
a = ?
Equation:
Equation: F = ma
F = ma
Newton’s 2nd Law tells us that when you accelerate (stomp on the gas) or decelerate quickly (brake fast) you use more force and wear out engine parts and brakes faster.
F = ma 50 = 10a 50 10
= 10 Ex. A force of 49 N causes a 7 m/s2 acceleration. Find the mass of the object it was pulling. Solve:
Solve:
Variables:
Solve: F = ma F = 50(40) F = 50 x 40
49 N = F 7 m/s2= a a
m = ?
F = 2000N
10a = 5m/s
2 Equation:
F = ma
F = ma 49 = m7 49 m 7 = 7 7 m = 7 kg
Ch.3:1 Name: Period:
1. F =
125 kilograms
Which of Newton’s Three Laws Applies?
2. m =
23 kgm/s
Law 1, 2, or 3?
3. a =
3 m/s2
___ When you put a book on a table the table pushes on the book.
4. v =
29 meters/sec
___ A person is pushed forward into their seatbelt when a car 5. D =
228 meters
stops.
6. p =
6 newtons
___ A larger car takes more force to move.
1. Inertia
A. An action that can causes motion.
___ A person leans on a wall and the wall pushes back.
2. Mass
B. Force pulling all object toward each
other.
___ A brick sits on a table until you push on it. 3. Gravity
C. The amount of matter in an object
Understanding Net Force 4. Net force
D. Total of all of the forces on an object.
Which way will it accelerate? 5. Force
E. Ability of an object to resist change of
motion.
30 N M 25 N Number these from least (1) to most (5) inertia.
A baseball A small
car
A truck A feather A large
train
6 N M 8 N Number these from least (1) to most (5) momentum.
Fast car Parked
Slow car Fast
Fast
15 N M 15 N truck
baseball
feather
A sled is being pulled to the left by 5 dogs, each dog pulling with
A 20 kg bike accelerates at 10 m/s2. With what force was the 6 Newtons of force. Find the net force.
person pedaling?

If a person pulls on a cart to the right with a force of 10 N and a
If a person is pushing a cart with a force of 40 Newtons and it second person pulls to the left with a force of 3 N, what is the net
accelerates at 0.5 m/s2, what is the mass of the cart? force (+ direction) on the cart?

A 2 N and 6 N force pull on an object to the right and a 4 N
What is the acceleration of a 3 kg rock that is thrown with a force force pulls to the left a 0.5 kg object. What is the net force on
of 18 N? the object?