Transcript Impulse and Collisions

Impulse
Impulse

In certain martial arts, people practice
breaking a piece of wood with the side of
their bare hand.

How can this be done without injury to the
hand?
Impulse
A
change in momentum created by a
force exerted over time is called
impulse.
 Basically,
impulse is a change in
momentum.
Impulse
If the momentum of an
object changes, either the
mass or the velocity or
both change
Impulse
Which do you think is
more likely to change:
the mass of an object, or
the velocity of an object?
Impulse
If the mass remains
unchanged, which is most
often the case, then the
velocity changes and
WHAT occurs?
Impulse
Acceleration
Impulse
What produces
acceleration?
Impulse
Force
Impulse
The greater the force acting
on an object, the greater its
change in velocity, and
therefore, the greater its
change in momentum
Impulse
How
long the force acts is
also important.
If
you apply a brief force to a
stalled car you changed the
car’s momentum.
Impulse
If you applied the same force
over an extended period of
time you will produce a
greater change in the car’s
momentum.
Impulse
A force sustained for a longer
time produces more change
in momentum than does the
same force applied briefly.
Impulse
BOTH Force and Time are
important in changing
momentum.
Impulse
In physics, the quantity
Force • time is known as
impulse.
Impulse
Impulse = change in momentum
This is how it looks on your STAAR chart:
Units?
Impulse
Impulse - examples

In certain martial arts, people practice
breaking a piece of wood with the side of
their bare hand. How can this be done
without injury to the hand?

Using your new found understanding of
impulse, what is your answer to this
question now?
Impulse - examples
In order to break wood with the hand, a
large force is applied in a short time. If
the hand bounces, an even greater
impulse is applied because there is a
greater change in momentum.
The martial artist must take care to strike
the wood with the fleshy side of the hand
so that there is a smaller force applied to
the hand than there would be if the
fingers or knuckles were to hit the piece of
wood.
Impulse - examples
 An
egg dropped on a tile floor
breaks, but an egg dropped on a
pillow from the same height does
not.
 Why?
Impulse - examples

In both cases, the mass and velocity are
the same. In this type of example, if the
amount of time the object is in contact
with the force goes up, then the amount
force goes down.

When dropped on a pillow, the egg starts
to slow down as soon as it touches the
pillow. The pillow increases the amount of
time it takes the egg to stop.
Impulse - examples

Boxers attempt to move with an
opponent’s punch when it is thrown. In
other words, a boxer moves in the same
direction as their opponent's punch. This
movement may prevent a knockout blow
being delivered by their opponent. Explain
how.
Impulse - examples
If the force applied by the opponent's
punch can be extended over a longer
time, the force of the blow is reduced,
minimizing the chances of a knockout
punch being delivered to the boxer.
Impulse
In a physics demonstration, two identical balloons
(A and B) are propelled across the room on
horizontal guide wires. The motion diagrams
(depicting the relative position of the balloons at
time intervals of 0.05 seconds) for these two
balloons are shown below.
Impulse
Which balloon (A or B) has the
greatest acceleration? Explain.
Impulse
Balloon B has the greatest acceleration.
The rate at which the velocity changes is
greatest for Balloon B; this is shown by the
fact that the speed (distance/time) changes
most rapidly.
Impulse
Which balloon (A or B) has the greatest final
velocity? Explain.
Impulse
Balloon B has the greatest final
velocity. At the end of the diagram, the
distance traveled in the last interval is
greatest for Balloon B.
Impulse
Which balloon (A or B) has the greatest
momentum change? Explain.
Impulse
Balloon B has the greatest momentum
change. Since the final velocity is greatest
for Balloon B, its velocity change is also the
greatest. Momentum change depends on
velocity change. The balloon with the
greatest velocity change will have the
greatest momentum change.
Impulse
Which balloon (A or B) experiences the
greatest impulse? Explain.
Impulse
Balloon B has the greatest impulse.
Impulse is equal to momentum change. If
balloon B has the greatest momentum
change, then it must also have the greatest
impulse.
Impulse – practice problem
A net force of 25 newtons is applied to a 20
kilogram cart for 2 seconds?
What is the impulse?
What is the change in momentum?
Impulse – guided practice
A net force of 30 newtons is applied to a 10
kilogram cart that is already moving at 1
meter per second. The final speed of the
cart was 2 meters per second. For how long
was the force applied?
Impulse – practice problem
A net force of 50 newtons is applied to a 20
kilogram cart that is already moving at 1
meter per second. The final speed of the
cart was 3 meters per second. For how long
was the force applied?
Impulse – practice problem
A net force of 40 newtons is applied to a 14
kilogram cart that is already moving at 1.2
meters per second. The final speed of the
cart was 3.4 meters per second. For how
long was the force applied?
Impulse – practice problem
A net force of 60 newtons is applied to a 35
kilogram cart that is already moving at .5
meters per second. The final speed of the
cart was 7 meters per second. For how long
was the force applied?
Impulse – practice problem
A net force of 100 newtons is applied to a
12 kilogram cart that is already moving at 5
meters per second. The final speed of the
cart was 20 meters per second. For how
long was the force applied?
Impulse – practice problem
A net force of 70 newtons is applied to a
100 kilogram cart that is already moving at
1.1 meters per second. The final speed of
the cart was 3.3 meters per second. For
how long was the force applied?