Impulse: Force-Time
Graphs
This is a force-time graph which
shows us the amount of force
applied as a function of time.!
What meaning does slope have for us in this graph?!
Well, let’s look at the impulsemomentum equation that we
practiced with last week.!
If we look at the area under the
curve, we get an interpretation
that is more meaningful.
As we can see the area under
the curve for a force-time graph
is equal to the impulse.
Remember that impulse is also
equal to the change in
momentum.
Example 1
— For the graph shown before,
assume that it shows a constant
force of 25 N acting over a 10 s
period of time. Determine the
impulse.!
— We could have simply use Δp = FΔt to figure out the impulse.
We could do this in this situation
because the force is constant.!
—  If we need to do a question where
the force is not constant, we can still
use the area under the line to get
the impulse, even though the
formula Δp = FΔt can not be used.!
Example 2: I am in a car that is accelerating from rest at a
red light. I want to calculate the impulse that is acting on
the car during the first 6 s. If I know that the force on the
car steadily increases from 0 N to 3000 N over this time,
determine the impulse. If the mass of the car is 1500 kg,
also determine the final velocity of the car.
3000 N
6s
Example 3: This graph shows the result
of applying 500 kg*m/s of impulse to an
object as it moved across the floor for
10.0 s. Determine the maximum force
that was exerted.!
— Even if the graph is a curved line,
you can still at least estimate the
area under the graph.!
An object of mass m = 2.0kg
experiences a force in Newtons
according to the Force vs. time graph
shown here. For the time interval
shown, what is the total change in
momentum of the object?