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# 12.7: Unit 10 Lab- Energy in Explosions

## Simulated Explosion

### Materials:

• lab sheet and writing utensil
• calculator
• for distance learners, access to online forums, videos, and help features for the spreadsheet software will likely be necessary
• “frictionless” track + two carts with velcro bumpers and at least one with integrated spring
• force probe
• two motion sensors + computer with sensor control and analysis software (or one motion sensor and one self-tracking motion cart).
• force probe

### Explosions

During an explosion, such as that which occurs within the cylinders of internal combustion engines, _______________________energy is converted into ___________________energy and ________________________energy.

### Observation

Typically after an explosion things are moving which were not moving before. Therefore, it seems like kinetic energy and momentum might not b conserved during explosions.

### Questions

Do explosions conserve kinetic energy?

Do explosions conserve momentum?

### Search Existing Knowledge

Find information about whether or not momentum and kinetic energy are each conserved during an explosion. Cite your sources.

### New Question

If the “explosion” is caused by a release of elastic potential energy instead of chemical potential energy, does that change any of the answers you found above?

### Hypotheses

Form two hypotheses regarding conservation of momentum and conservation of kinetic energy during a simulated “explosion” created when an object is broken in half by releasing a spring that was compressed between the two halves of the object. As part of your hypotheses, draw diagrams of this situation before and after the “explosion” occurs.

### Test

Place the two carts together with the loaded spring in the first cart facing the second cart. Record the motion of both carts while pushing the spring release button. Use a ruler to tap the button from directly above, making sure not to put any horizontal force on the button/cart.

Use your velocity data to determine the velocity of each cart immediately after the explosion has finished, but before the carts begin to slow down due to friction. Be sure to consider that the velocities should have opposite directions, but that your motion sensors will not necessarily record the correct directions. You will need to choose a positive and negative direction for your experiment and correct the directions recorded by your sensors accordingly. Record your final velocities for each cart below.

Measure the mass of each cart and record below:

### Momentum Analysis

What was the total momentum of the system before the “explosion?”

Calculate the total momentum after the explosion.

### Kinetic Energy Analysis

What was the kinetic energy of the system before the explosion?

Calculate the total kinetic energy after the explosion.

### Kinetic Energy Conclusion

Was kinetic energy conserved in this explosion?

If kinetic energy was not conserved in this experiment, did it increase or decreases?

What type of energy was converted into kinetic energy during this experiment?

### Efficiency Analysis

Let’s find out the efficiency of this “explosion” at converting elastic potential energy into kinetic energy. First we need to know how much elastic potential energy was contained in the spring and to calculate that we need to know the spring constant and compression distance.

Measure the compression distance with a ruler and record here:

Use a force probe to measure the force required to compress the spring to half of the compression distance. Record the distance and force here:

Calculate the spring constant of the spring.

Calculate the elastic potential energy stored in spring when fully compressed.

Calculate the efficiency of the “explosion” at converting spring potential energy into elastic potential energy.