AP PHYSICS 1-Algebra Based NAME: UNIT: AP Physics 1 Review ...
Plan for Today (AP Physics 1)
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Transcript of Plan for Today (AP Physics 1)
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Plan for Today (AP Physics 1)
• Go over tests• Lecture/Notes on Work and Energy
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Test Results
• Average: 86.6• Without the curve: 82 percent• 25 As
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Students do the following. . .
• Curl a bowling ball 10 times• Take a bowling ball to the water fountain and
back • Push a brick across a table
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Vote
• Which student did the most work?
• Only one to do work
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Equation
• Work = Force times distance times cos angle• Work = F x cos 0• Units: • N*m• Kgm/s^2 *m = kgm^2/s^2• Joules – energy
• This is a scalar quantity– No direction
• Note: Physics definition of work• Very narrowly defined
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• Why do you need cos in the equation?• Force must be in the DIRECTION of motion
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Example using Angles
• If we pull a brick with 20 N of force at a 25 degree angle above horizontal for three meters, how much work is done?
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Example using Angles
• If we pull a brick with 20 N of force at a 25 degree angle above horizontal for three meters, how much work is done?
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Example using Angles
• If we pull a brick with 20 N of force at a 25 degree angle above horizontal for three meters, how much work is done?
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Situations
• Carry a brick across the room• Was any work done?• No• Force and displacement in different directions• No change in its energy• Velocity and height don’t change
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Situations
• Carry a brick across the room• Was any work done?• No• Force and displacement in different directions• No change in its energy• Velocity and height don’t change
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Situation
• What if I pick a brick straight up?• Force of hand is like the normal force• In same direction as the distance traveled• So yes, work is done• Work is positive
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Situation
• What if I pick a brick straight up?• Force of hand is like the normal force• In same direction as the distance traveled• So yes, work is done• Work is positive
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Situation
• Pushing a rolling chair and allowing it to roll to a stop
• What happened?• I put energy into the chair• Force times distance applied = work• What happens to the energy?• From my work it converts to kinetic energy• What happens to KE?• Does this energy disappear?
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Chair situation continued
• What happens to the kinetic energy?• We did work, it had kinetic energy, but then it
stopped
• Work done • Kinetic energy converted to what?• Heat from friction
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Chair situation
• The work done by friction opposed motion• So the work is negative
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Generalization
• Negative Work slows down• Positive work speeds up
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Example
• A 10 kg mass moves 5 m. The coefficient of friction is .2.
• What is the net work if a force of 40 N is applied at 30 degrees above horizontal?
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Work KE Theorem
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Work KE Theorem
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Work KE Theorem
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Work KE Theorem
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Work KE Theorem
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Work KE Theorem
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Work KE Theorem
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What did this mean?
• What is ½*m*v^2?• KE = ½*m*v^2
• Are we sure this is correct?• How should we check?• Units!• KE = (kg)(m/s)^2 =kgm^2/s^2• What is this?• Joules!
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Example
• A car with a mass of 1000 kg starts at 10 m/s and accelerates to 20 m/s in 50 m.– How much work is done?– What force is required?
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• 150000• 3000