Student Exploration: Ants on a Slant (Inclined Plane) (ANSWER KEY)

Vocabulary : friction, inclined plane, work
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. Imagine you w ere lifting very heavy jugs to the top of a house. You can either use the stairs on the left or push them up the inclined plane on the right. Which option is easier? Why?
2. If a person in a wheelchair wanted to get to the second story of a two-story building, would it be easier to take a short, steep ramp or a long, shallow ramp? Explain
Gizmo Warm-up
1. In the Ants on a Slant Gizmo™, ants use a slanted stick to help push food to the top of a tree stump. Drag the stick sideways to change its steepness. Change the number of ants by dragging them to the item. Then click Play ( ) to see if the ants can lift the item. First, describe a strategy to find out which items are heavier than others
2. List the food items in order, from lightest to heaviest, using your method:
Question: What are advantages and disadvantages of using inclined planes to help lift?
1. Observe : Run a few trials with the Gizmo. Explore both shorter (steeper) and longer (flatter) sticks. Why do you think people (or ants) would choose to use an inclined plane to help lift?
2. Predict : Make two predictions below. (Stick lengths in the Gizmo: 10, 15, 20, 25, and 30 cm.)
A. Which stick length will let you lift a peanut with the f ewest ants? 
B. Which stick length will require the l ongest time to lift a peanut? 
3. Experiment : Test your predictions. Use all five stick lengths to lift a peanut. List results here.
4. Draw conclusions : Name an advantage and a disadvantage of using an inclined plane.
5. Analyze : The stick doesn’t just support the peanut; it actually p ushes up on it! (Think of what would happen if the stick suddenly disappeared.) This pushing up is what “helps” the ants
A. Which kind of inclined plane pushes up m ore? (Circle one.) 
B. What do you think causes this
Question: How does length of an inclined plane affect the force needed to lift an object?
1. Form hypothesis : Suppose you already know how many ants it takes to lift an object straight up (using the 10-cm stick). How can you predict the number of ants that will be needed to lift the object with an inclined plane of a certain length?
2. Collect data : How many ants can lift the blueberry straight up (using 10-cm stick)?
3. Predict : Use your hypothesis to predict what is the smallest number of ants required to lift the blueberry on sticks of other lengths
4. Experiment : Test your predictions in the Gizmo. How many ants are needed for each?
5. Calculate : The work used to lift an item equals the force needed times the distance moved. You can estimate work by multiplying the number of ants times the stick length
6. Draw conclusions : How does using an inclined plane affect the work required to lift an item?
Question: How does friction affect an object sliding on an inclined plane?
1. Explore : Use the Gizmo to examine the effects of friction. Run several different trials.
A. Are there times when friction helps the ants
B. Are there times when friction prevents the ants from lifting the item
2. Investigate : Select the blueberry. Run the test on the 10-cm, 20-cm, and 30-cm sticks. Record the minimum number of ants needed w ith friction, and also w ithout friction
3. Analyze : Friction causes work to be “wasted” as heat (which is why your hands get warm).
A. Does friction waste more work on longer or shorter planes
B. How can you tell
C. Why do you think this is? [Hint: Remember the stick presses up on the item. Do your hands get warmer faster if you press them together harder as you rub?]
4. Conjecture : Does friction cause more energy to be wasted if the object is heavier? Why?
Use the Gizmo to test this. Describe your results in your notebook or on a separate sheet.

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