Names: ______

PHYSICS

Hooke’s Law PhETLab

Purpose:

  1. To investigate Hooke's Law (The relation between force and stretch for a spring) F = -kx
  2. To re-visit Newton's 3rd Law of Motion.

Discussion:

Everybody knows that when you apply a force to a spring or a rubber band, it stretches. A scientist would ask, "How is the force that you apply related to the amount of stretch?" This question was answered by Robert Hooke, a contemporary of Newton, and the answer has come to be called Hooke's Law.

Hooke's Law, believe it or not, is a very important and widely-used law in physics and engineering. Its applications go far beyond springs and rubber bands.

You can investigate Hooke's Law by measuring how much known forces stretch a spring. A convenient way to apply a precisely-known force is to let the weight of a known mass be the force used to stretch the spring. The force can be calculated from W = mg. The stretch of the spring can be measured by noting the position of the end of the spring before and during the application of the force.

Equipment:

PhET Simulation Masses and Springs

Procedure:

  1. Go to PhET web address above and run the simulation.
  2. You will need to recordthe mass that you hang from the spring and the change in position of the end of the spring before and after the mass is added. I created a data table for you below. From this, you will calculate the force applied to the spring. You will do three trials using Spring #3, set to the default setting for stiffness of the spring.Place each of the masses from the spring and record your data. (Use 50 g, 100 g, and 250 g)
  3. For each trial, record the mass, the starting position of the spring (before hanging the mass) and the ending position of the spring (while it is being stretched) and record the change in position as displacement. The ruler can be dragged to Spring #3 and aligned with the starting position of the spring at rest. It’s easier to determine the position of the stretched spring that way.
  4. Using the slider for spring softness on the right side of the screen, repeat the process using Spring #3 two more times first setting the softness to soft (not all the way left but at two notches over) and then to hard (all the way to the right)

Part 2: Spring Softness: Semi-Soft
Trial / mass (g) / mass (kg) / force applied (N) / Displacement, stretch (converted to m)
1
2
3
Part 3: Spring Softness: Hard
Trial / mass (g) / mass (kg) / force applied (N) / Displacement, stretch (converted to m)
1
2
3

Data:

Part 1: Spring Softness: Average
Trial / mass (g) / mass (kg) / force applied (N) / Displacement, stretch (converted to m)
1
2
3

Calculations:

  1. Calculate the force applied to the springs in each trial (W = mg) Use g = 9.8 m/s2. Mass must be in kg. Place the answer in the data table above.
  2. Using Graphical Analysis, create a “Force versus Displacement” graph for each part above. Be sure to use force in newtons and displacement in meters. Also, make sure you follow the proper set up for graph construction. (Force will go on the why access, shout out).
  3. Find the slope of theline on graph using the regression line button on GA (seen on the right, it can be found on the menu bar).
  4. Insert your graph below (right click copy on graph, right click paste on this document).

Graphs:

Questions:

  1. Imaging hanging an object (at rest) from the spring scale. Draw free body diagram that shows all of the forces that act on the object.
  1. If the object is at rest, what is the net force acting on it?
  1. Are the forces that act on the object equal and opposite? Are they a Newton's Third Law force pair? Explain.
  1. What is the relationship of the force on the spring and stretch of the spring?
  1. What value and unit did you get for the slope and what does the slope of the graph represent?

Part / “Slope”
Part 1: Softness of Spring: Average
Part 2: Softness of Spring: Semi-Soft
Part 3: Softness of Spring: Stiff
  1. What is a real-world application of Hooke’s Law? On other words, why is it important (give a specific example)? You can research the uses of springs using the internet to come up with an answer. Think about the differences in each spring and how engineers would rely on that information. Give me a good answer—like a really good application—please don’t give me it is useful when Ross builds his mattress out of pen spring and becomes a millionaire. That is silly.