

Mouse Trap Spring Potential Energy
Name: Dan
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
How do I calculate the potential energy of a mouse trap
spring?
Replies:
Educator,
In most cases, there is no easy formula to calculate potential energy.
As a great deal of energy is lost to sound, it may not even be
conservative. I will use language that assumes you are using a
traditional mousetrap. Still, the method is very general.
If you want a precise measurement, then use a device that can measure
force, something that can handle whatever force is needed to hold the
trap in its set position. Keeping the scale or sensor directed parallel
to the path, measure the force needed to hold the trap still at various
points along the path. Use distance along the circumference as your
distance measure. Be sure to note that zero position is NOT zero force.
For zero, use the force needed to barely lift the trap from the wooden
base. For safety, be sure the base is clamped in place.
Graph force as a function of position. Calculate the area under the
curve. You may even be able to estimate it as a triangle. For your
scale use Newtons, NOT kilograms. Many scales are unfortunately marked
in kilograms for convenience to grocery workers. Use meters for your
distance along the circumference. The area under the curve will be in
Joules.
If you want an approximate value, assume that the mousetrap will operate
as a spring. The work done to set the spring, and thus the potential
energy will depend on two quantities: average force and total distance.
Find the force at the start, that which is just enough to open the trap.
Find the force that is just enough to hold it in position near the end.
Calculate the distance along the circumference, start to finish.
0.5*(F_start+F_end) is your average force. Multiply this by the total
distance along the circumference (perhaps pi*radius). Now you have an
excellent approximation for the potential energy in a set mousetrap.
Dr. Ken Mellendorf
It is not so easy to calculate, but you can measure the force required
to stretch the spring as a function of the displacement by hanging known
weights from the "trap" end of the mousetrap and measuring how much the
spring is wound up. You will want to take safety precautions in the event
a weight should "slip" because you could get a nasty bruise, or even a
broken finger if something should slip. You can obtain the potential
energy directly from the weight and the displacement of the trap. You can
find the formulas on any web site using the search term(s): Hooke's Law
potential energy. There are a couple of ways to manipulate the
measurements depending upon how you set up the experiment.
Vince Calder
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Update: June 2012

