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