Author: Lee Trampleasure

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11/13 Force diagrams: Two solved problems

Force diagrams, or Free Body Diagrams, are sketches we use in physics to show forces applied to an object or system of objects.

Here are a couple of videos I created to help walk you through some complicated problems. I encourage you to pause them as you go through and see if you can determine the ‘next move.’

Problem A

A 13 kg block of wood slides across the floor with constant speed when it is pulled with a horizontal force of 32 N. What is the friction constant, µ, between the wood and the floor?

Problem B

A block is sliding up a wall with a constant velocity, and a force applied upwards at an angle. Here is a sketch:

sketch showing the box on the wall with the unknowns labeled.
As with many AP questions, you are asked to solve for one variable in terms of the others. In this case, your final equation should be in the form F = (an expression that includes m, μ , and θ )
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10/22 Identifying circuits that will work

Look at the circuits below. In only one of them will the bulb be lit. Sketch the one circuit that will work, and explain how it is different than the others.

  • Circuit A will not work because the switch is open.
  • Circuit B will not work because the switch is open and there is a wire missing on the top left side.
  • Circuit C will not work because there is a small gap in the wire between the bulb and the magnet wire.
  • Circuit D will work!
  • Cicuit E will not work because it is missing a battery, so there is no energy in the circuit.
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10/21: Creating magnets with electricity

In this activity, groups created magnets by creating a circuit that included magnet wire wrapped around a large nail. The results were:

  • The greater the number of wraps around the nail, the stronger the magnet—the more staples it could pick up.
  • To make the circuit work, you need to have a complete path of wire from one side of the battery to the other.