In thought
Which of the following do you think would deliver a greater
force when colliding with a wall? A golf ball moving at 70
m/s or a baseball moving at 50 m/s? Explain your answer
in 3-4 sentences.
Objectives
State Newton’s second law of motion and explain how force
and mass are related to acceleration
Key Term
Newton (N)
Newton’s Second Law of
Motion
THE NET FORCE ON AN OBJECT IS EQUAL TO THE
PRODUCT OF ITS ACCELERATION AND ITS MASS
FORCE = MASS x ACCELERATION
F = ma
IMPORTANT
F = ma
Acceleration is measured in meters per second per second
(m/s2)
Mass is measured in kilograms (kg)
Force = kg x m/s2
One newton (N) is equal to the force required to accelerate
one kilogram of mass at one meter per second per second
a = F/m
Acceleration of an object can be found if you know the force
measured in newtons and the mass of the object
A = F/m
A = m/s2
F=N
m = kg
Force Practice Problem
A 52 kg water skier is being pulled by a speedboat. The force causes the
skier to accelerate at 2 m/s2. Calculate the net force that causes this
acceleration.
F = ma
Force = 52 kg x 2 m/s2
Force = 104 kg x m/s2
Force = 104 N
Force is
measured in
NEWTONS
Force Problems
What is the net force on a 2,500-kg elevator accelerating at 2.3 m/s2?
Force = 5,750 N
What net force is needed to accelerate a 55-kg cart at 17 m/s2?
Force = 935 N
Changes in Force and Mass
One way to increase acceleration is to increase the force
According to F = ma, when force increases the acceleration
also increases
Another way to increase acceleration is change the mass
Mass and acceleration have an inverse relationship, meaning
if one goes up the other goes down
Review
Force = mass x acceleration
If force increases so does the acceleration
If mass increases acceleration decreases
References
Anderson, M. et all (2012) Physical Science. McGraw-Hill:
Columbus
Frank, D.V et al (2001). Physical Science. Prentice Hall: New
Jersey
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