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  1. Tom Hammer

    Measurement of speed using redshift or blueshift

    You are contradicting yourself. Yes, sound that you hear that is higher than normal = coming toward you. Light that is shorter wavelength (bluer) also means coming toward you.
  2. Tom Hammer

    Supporting a trapezoid between two wedges

    Yes, thank you. But I am having trouble drawing a force diagram which makes sense at the two surfaces of B.
  3. Tom Hammer

    Supporting a trapezoid between two wedges

    Let Nr = normal force on the right side of the trapezoid B and Fr = the force of friction on the right side of B. Let Nl = normal force on the left side of B and Fr = the frictional force on the left surface of B so Nr = 5 sin45 and Fr = 5 sin45 = and Nl = 5 sin 60, Fl = 5 sin 30.
  4. Tom Hammer

    Looking for used physics lab/demo equipment

    Hi, I'm looking for used physics lab/demo equipment that you might personally own and are looking to sell. I'm starting to do science with the grand-daughters, and buying everything new would be expensive. Things like: bunsen burner for propane, compasses, iron filings, bi-metallic strip, or...
  5. Tom Hammer

    An apple falls from a tree, Does the moon move as a result?

    I am interested in the following thought experiment: an apple falls from a tree on Earth. Does the moon move (although slightly)? I can see an argument for it doing so—the center of mass of the Earth has moved slightly away from the moon, so the moon would feel a slightly smaller force and would...
  6. Tom Hammer

    Help please -- Amplitude of a spring - does it change with mass?

    I think this is easiest solved using energy. Potential energy (PE) of the spring when compressed at (b) = KE of both objects at (c) = PE of spring + KE of sliding object in (d)
  7. Tom Hammer

    Direction of acceleration of an incline

    Yes. There are two forces on M. One, the force of gravity on M is perpendicular to the horizontal, so it has no component to the left or the right. m is sliding to the left. The force of friction ffMm (the force of friction of M on m is up the incline, in the opposite direction of the velocity...
  8. Tom Hammer

    Direction of acceleration of an incline

    The net force on M is to the left, not to the right.
  9. Tom Hammer

    The coming revolution in physics education

    I taught high school physics for 15 years with some success. The difficulties were not in solving problems once the underlying physics was understood but in undoing the years of “false physics” that most students arrived having internalized. In the 90s there was a movement to measure the basic...
  10. Tom Hammer

    I Was the recent ISS leak imminently dangerous?

    The ISS suffered a leak apparently caused by a 1/8 inch hole left during manufacture and never repaired. On Quora, the claim has been made that such a hole with one atm of pressure difference would only cause 324 cu ft of air to rush out per hour. I don't think this is close to correct, but I am...
  11. Tom Hammer

    B Stairmaster physics

    Let us consider climbing an incline on Earth that is the same angle as the stair climber and is parallel to the Earth's motion through space around the sun. Obviously relative to the sun the incline is moving. Let us approximate that the velocity is constant. The hill climber does not notice...