First Law of Thermodynamics

Forms of Energy

• Potential Energy
• Spring PE = 1/2 kx² (where Hooke's Law: F=kx)
• Gravitational PE = mgh

• Kinetic Energy
• KE = 1/2 mv²

• How does a toy dart gun work?

The Nerf toy guns provided use a spring to launch the projectile. Using your knowledge of the First Law of Thermodynamics, predict the velocity that the projectile leaves the barrel of the toy gun and the maximum height the projectile can reach.

After making your predictions, experimentally verify the maximum height and velocity and calculate the efficiency (η) of your device at converting PEspring to Pedart using the formula below:

η= h_experimental/h_theorical

Lab Documentation

• A problem statement.

• State any assumptions that you make during your calculations.

• One assumption is that your spring is linear with constant k value

• List your governing equations

• Record your measured values

• Deflection of spring, mass of bullet, force applied to spring

• Multiple test (at least 10) should be preformed for measured values so that outliers can be eliminated and a decent average can be found.

• Data should be in tabular form

• Provide your calculations for velocity and maximum height predictions.

• Show all units with your values

• Watch for needed unit conversations and use engineering default of 3 significant digits

• Answers should be boxed

• Document the procedure used to verify the maximum height and record all results (at least 10 data points in tabular form)

• Provide your calculations for efficiency

• Report your conclusions of the Lab. Explain the low efficiency of the gun. How could the gun be modified to improve efficiency? How could your calculations have better predicted actual results?