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