Push ‘n Go
A little push can go a long way.

Concepts
Work, energy, controlled experiments, graphing, analyzing data

Materials
  • Push-N-Go
  • Spring scale (use the Newton or N scale)
  • 50 and 100 g masses
  • 2 meter sticks

Procedure
1. Push the head of the Push-N-Go down and let it go. Observe how the work you do on the Push-N-Go causes it to move. Record your observations below:


2. Estimate how much force you push down on the head of the Push-N-Go by comparing your push on a spring scale. Record the force you estimated in Newtons (N):


3. Measure how far the head goes down. Convert this distance to meters. Show all your work.


4. Calculate the work you performed on the Push-N-Go. Work can be calculated by multiplying the force by the distance. Mathematically this is written as work = force · distance. The units of force are Joules (J), and the force must be in N and the distance in m. Show your work.


5. Now design and conduct an experiment to see how adding mass affects the distance a Push-N-Go travels. In your experiment test adding 0, 50, 100 and 150 grams to the Push ‘n Go and measure how far it travels. Record your data in the table below.

figure19.jpg
Figure 19: A Push 'n Go with a 50 gram mass in the back of it.


Added Mass (g)
Distance (cm)
0

50

100

150



6. In a controlled experiment only one variable is changed to see if it affects the outcome of the experiment. What variable did you change to see its affect?


7. Create a Distance versus Added Mass graph.

8. Draw a best-fit line through the 4 data points so the line goes all the way to 200 g.

9. Answer the following questions:
A. What was the result of the work you performed on the Push-N-Go; that is, what happens after you push the head down?



B. What happened to the distance the Push-N-Go traveled as you added mass?



C. What can you conclude about the relationship between the mass added to the Push-N-Go and the distance it travels?
Hint: the more mass added to the Push-N-Go the more/less/same distance it travels?



D. Use your graph to predict how far the Push-N-Go will travel if you had added 200 g to it?



E. Is your prediction in Part D an example of interpolation or extrapolation? Explain your reasoning.



10. Write a proper Results & Discussion section for the Push-n-go experiment you performed. Be sure to include:
  • Data displayed in a graph with axes labeled and a caption under the graph
  • A discussion of the data – note any trends or relationships (direct, inverse or no); talk about the independent and dependent variables in your discussion
  • Include a discussion of the amount of work necessary to make the Push-n-go move forward (recall the equation you used)


Extension 1
Have students pick up and hold the Push ‘n Go so that they are not touching the wheels (the wheels need to be able to move freely). Next they should push down on the head and carefully watch which wheels spin as the head comes back up. Only one set of wheels will spin. Have the students make an inference to explain what is occurring on the inside of the Push ‘n Go.

As new observations are made an inference can change. One of the strengths of science is its willingness to change as more information is provided. Using a screwdriver take one of the Push ‘n Go’s apart and allow the students to observe what is on the inside. Have them revise their inference given these new observations.

This same activity can be done as a way to help students understand energy transformations or the change from potential to kinetic energy.

Explanation
Inside the Push ‘n Go is a spring and a series of four different gears, one of which is attached to the back wheels. When the head is pushed down a gear rack on the back of the little figure pushes down on the spring while simultaneously disengaging the gears they can’t spin the wheels. When the head is released the gear rack is pushed up by the spring but this time it engages all the gears and the wheels spin.

As long as the head of the Push ‘n Go is pushed all the way down every time, the Work done by the spring to move the Push ‘n Go is always the same. Given a constant amount of work, the addition of mass to the Push ‘n Go will cause it to travel a shorter distance. The more mass added to the Push ‘n Go the less distance it will travel. Once the Push ‘n Go is moving it is the force of friction that eventually causes it to slow down and stop. Given the inverse relationship between the amount of mass added to the Push ‘n Go and the distance traveled, a typical student graph should like as follows:

figure20.jpg
Figure 20: Typical table and graph of the data students will get when adding mass to a Push 'n Go

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