113 Unit 9 Lab: Energy in Explosions

Simulated Explosion

Materials:

• lab sheet and writing utensil
• calculator
• “frictionless” track + two carts with spring-loaded bumper
• two motion sensors  + computer with sensor control and analysis software (or one motion sensor and one self-tracking motion cart).

Outcome 9-1

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 even though nothing was moving before the explosion.

Outcome 9-2

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.

Hypotheses

We will simulate an explosion by releasing a spring that was compressed between the two objects, causing them to separate. This produces the same situation an explosion, specifically that things are moving afterward, even when nothing was moving initially. Form two hypotheses, one regarding conservation of momentum and conservation of kinetic energy during the simulated explosion. 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.

Momentum Conclusions

Does your experiment support or refute your hypothesis on momentum conservation?

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?

Does your result support or refute your hypothesis?

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?

Outcome 9-3

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.

If the efficiency was not 100%, why not? Where did the missing mechanical energy go?

How much energy was not converted to kinetic energy?

Outcome 9-4

Power Output

Use tour velocity data to determine the length of time over which the elastic potential energy was converted to kinetic energy. Record here:__________

Use the time interval you found and the final kinetic energy of the carts to calculate the kinetic power output of the spring during the explosion.

Use the time interval you found to calculate the thermal power output of the spring during the explosion.