2. Newton’s Second Law can be expressed with
an equation:
Which can be re-arranged to isolate Force
like this:

3. Force is measured in Newtons
A Newton = the amount of force needed to
accelerate a 1 kilogram mass at a rate of 1 m/s2
Since F = m.
a
1 N = 1 kg.
m/s2

4. 1. Describe the motion
of the object this
graph depicts
2. Using F = ma,
calculate the mass
of the object

5. 1. Describe the motion of the
object this graph depicts
the object is accelerating
2. Using F = ma, calculate the
mass of the object
using rise/run:
3N-1N/3m/s2
– 1m/s2
= 1 kg

6. If there is acceleration (speed up, slow down,
change direction), there is an unbalanced
force.
remember: another name for unbalanced
force is net force

7. Look at the relationship between force,
mass, and acceleration in this equation:
To keep the same acceleration, what must
force do if mass is increased?
 force must increase just as much

8. To be more specific:
 If acceleration stays constant and the mass
of the object doubles, what must the force
be doing?
 doubling

9. We already know that the formula for the
second law of motion is F = ma
We can use this formula to calculate the force
of weight
Weight = mass x accelerationgravity

10. It’s really, really important to remember:
a net force results in acceleration
BUT
no net force does not mean no motion – an
object will move at a constant speed in a
straight line with no net force!!!

11. The force required to accelerate a 2 kg
mass at 4 m/s2
is
 (a) 6N (b) 2N (c) 8N (d) 16N
Answer
 The correct answer is 8N because F = ma
and so F = (2 kg)(4 m/s2
)

12.  What force will be needed to accelerate a 8kg mass at
the same acceleration as a 4kg mass?
 (a) the amount of force does not change
 (b) the force needs to be 4x’s as much
 (c) the force should double
 (d) it will take half as much force
 Answer
 The correct answer is “the force should double” because
the mass doubled while acceleration was held constant.

13.  A cart has a constant acceleration from rest. The force
on the cart must be
 (a) decreasing
 (b) zero
 (c) constant
 (d) increasing
 Answer
 The correct answer is “constant” because a constant net
force creates a constant acceleration.