Rubber Band Lab

The BIG Question??
    - How can we store energy to do work for us later?
    - How does the force it takes to stretch a rubber band depend on the AMOUNT by which you stretch it?

 

• This week in Physics class, we tested how we are able to store energy that allows work to be done later. To test this, we used a rubber band and an air track that hooks up to an air vacuum. We took two trials, one with a single loop and another with a dooble loop. In order to answer our second big question, we had to measure the force in terms of distance. Once we put the rubber band on the air track, we hooked the electric force probe over both strands of the rubber band. Then we stretched the rubber band five different lengths and held it there for about ten seconds. To calculate the force, we averaged the values using "analyzing statistics." Then we recorded our data and repeated this process for both trials.

• Trial #1 with single loop:
• 1) 1 cm = 0.01 m = 0.538 N
• 2) 2 cm = 0.02 m = 1.341 N
• 3) 3 cm = 0.03 m = 1.710 N
• 4) 4 cm = 0.04 m = 2.693 N
• 5) 5 cm = 0.05 m = 3. 372 N

• Trial #2 with double loop:
• 1) 1 cm = 0.01 m = 3.835 N
• 2) 2cm = 0.02 m = 6. 375 N
• 3) 3cm = 0.03 m = 8.605 N
• 4) 4cm = 0.04 m = 11.313 N
• 5) 5cm = 0.05 m = 12.782 N

• In order to analyze our data, we graphed these points on a line graph for Trial #1. The force, measured in Newtons, went along the y-axis, and the amount of stretch, measured in meters, along the x-axis.

• Once we graphed our data, we had to derive an equation from y = mx + b, using the variables F, K, and X.  So we found the slope of our line, which was 70.85 (Newtons/Meters). We found that the slope of our line is our elastic constant "K". We found that Force (F) and the distance stretched (X) were directly proportional. Then we plugged in variables and got F = KX.

• Now we had to find the energy. As we saw in the Pulley Lab, to find the energy, we need to find the area of a certain part on our graph. In the Pulley Lab we found the area of a rectangle (A = LH) or (W = FD). Now in this lab, we have one line, so to find the area we created a triangle from that one line, using it  as our hypotenuse.

• The area of a triangle is A = (1/2) BH. To relate the equation to our experiment, We plugged in "U" for "A" which stands for the elastic potential energy. The base of our triangle is "X", the distance stretched, and the height would appear to be Force "F"

• U = (1/2)  XF

• Since we already found what the equation for Force is, all we have to do is plug that equation in for F in our new equation.

• U = (1/2)  X (KX)
• or U = (1/2)  K (Xsquared)

• In conclusion, we found that potential energy is the energy stored that does work for us later. In this case, as we pull back the rubber band, potential energy is stored, which enables us to flig the rubber band after we let go.

• Watch this video about potential energy!

• Real World Connection: Ever jump on a trampoline before?? If you have, ever wonder what allows you to jump so high? Trampolines contain springs in them. When pressed down upon, elastic potential energy is stored and it releases. It allows you to jump higher and higher and you put more force on the trampoline. Elastic potential energy is what makes a trampoline so fun to be on!