## Can Crushing Experiment

#### Learn the different between a static and a dynamic force while recycling an aluminum can in this can crushing experiment.

Showing kids the force needed to crush an aluminum can is a nice demonstration of some simple principles of physics.

Experiment Rating

Difficulty
Supplies

Items Needed:

• Brick or heavy flat rock about the size of a brick
• Several aluminum soda cans
• Scale to measure weight

EXPERIMENT STEPS

• #### Step 1

Measure the weight of the brick using the scale.  Record the weight in either pounds or grams.

• #### Step 2

Place an aluminum can on the floor.  Place the brick on top of the aluminum can.  Show the kids how the aluminum can supports the weight of the brick.  Explain how the strength of the aluminum material in the shape of the can cylinder is stronger than the force of the brick resting on top of the can.

• #### Step 3

Pick up the brick about 2 to 3 feet above the aluminum can.  Ask the kids what do you think will happen if you drop the brick.  Remind the kids that the brick was able to support the weight of the brick.  Measure the actual height of the brick above the top of the can to later calculate the force on the can.

• #### Step 4

Holding the brick directly over the aluminum can, drop the brick on the can.  Observe what happens.  Ask the kids the difference between the force of the brick when dropping the brick vs. the force of the brick while resting on top of the brick.

SCIENCE LEARNED

#### Can Crushing Experiment:  Static Forces

A static force is a force that is not moving.  In the can crushing experiment, the strength of the aluminum can easily supports the force of the brick.  With the brick resting on top the aluminum can, this problem becomes a simple static exercise.  Static equations apply to materials when there are not unbalanced forces on the object.  With the brick and can not moving, the forces balance.  The force the brick applies downward on the can is the weight of the brick.  The resultant force the aluminum can applies back on the brick is also equal to the weight of the brick.  The net force is zero.

#### Can Crushing Experiment: Dynamic Forces

By dropping the can on the brick, a different type of force called a dynamic force is now in action.  Dynamic forces result when something is moving.  In this case the brick is allowed to drop and gain speed from gravity.  Gravity is an acceleration, so the brick will accelerate until it hits the can.  The impact velocity is found from the following equation:

v= velocity of the brick at impact in ft/sec or km/sec

g = value of gravity, 32.2 ft/sec2 or 9.81 km/sec2

h = height of brick before it is dropped in feet or meters

We know that the higher we drop the brick, the more force it will apply to the can.  To consider the speed and the mass of the brick, calculate its kinematic energy.  The kinematic energy of the brick is equal to the following equation:

KE = 1/2 mv2

KE = kinematic energy of the moving brick

m = mass of the brick

v = velocity of the brick (calculated above)