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Material Type: Notes; Class: How Things Work; Subject: Physics; University: University of Illinois - Urbana-Champaign; Term: Unknown 2007;
Typology: Study notes
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Zip met his fate in free fall …
You have to aim straight at the monkey, even if the dart goes slowly… note: this animation is not accurate Everything falls with the same acceleration!
Observations About Ramps
A ramp makes lifting a box easier because… A) You can use less energy to lift the box B) The ramp exerts some force on the box C) A ramp lets you use wheels Forces Present On the table (and the ball) due to the weight of the ball (mg) W=mg On the ball due to the support from the table (Fsupport) These forces have the same magnitude for a ball that’s not accelerating Fsupport Newton’s Third Law For every force that one object exerts on a second object, there is an equal but oppositely directed force that the second object exerts on the first object. To every action there is an equal and opposite reaction This can be hard to believe sometimes! But you can’t escape it
Weight or mg Support Force or Fsupport Net Force along ramp Force from box on ramp perpendicular to surface
Weight or mg Support Force Force along ramp from weight You have to apply a force that’s smaller than the weight to accelerate the box
You always have to do the same amount of work W=F d Work is defined as the force parallel to the displacement times the displacement: W = F ll x d Work = Force(along direction of motion) x distance Straight Lifting: 300 lb. x 6 ft. = 1800 ft-lbs Up Ramp: 90 lb. x 20 ft. = 1800 ft-lbs (same work, less force)
Here’s another way to understand why you can’t win The box has to be lifted by 6 ft, and gravitational potential energy = mass ×g × height And work is all about transferring energy!
The work done is: W = m g h = force x distance = change in gravitational potential energy
