Friday, May 30, 2008
Thursday, May 29, 2008
Thursday, May 29, 2008
Went over questions on Circular Motion Problem sheet.
Quiz on Circular Motion requiring a Zap!
Went over quiz.
Started Hewitt video on Gravity.
Quiz on Circular Motion requiring a Zap!
Went over quiz.
Started Hewitt video on Gravity.
Wednesday, May 28, 2008
Wednesday, May 28, 2008
Answered any questions on RA 7.4
Collected RA 7.4
Circular Motion Quiz
Went over Quiz
Students worked on Circular Motion Problems.
Graded and handed back RA 7.4 and Circular Motion Quiz. Talked to each student individually, explained corrections to work and answered any remaining questions.
Collected RA 7.4
Circular Motion Quiz
Went over Quiz
Students worked on Circular Motion Problems.
Graded and handed back RA 7.4 and Circular Motion Quiz. Talked to each student individually, explained corrections to work and answered any remaining questions.
Tuesday, May 27, 2008
Tuesday, May 27, 2008
Collected Circular Motion Lab Reports
Uniform circular motion - Motion in a circle at constant (uniform) speed.
Showed using definition of acceleration, a = (vf-vi)/t and adding the vectors using the parallelogram rule that for uniform circular motion, the acceleration is directed towards the center of circle.
Since there is an acceleration directed towards the center of the circle, and F = m*a, there must be a force also directed towards the center of the circle. The acceleration is ALWAYS in the direction of the net force. There must be an acceleration since the direction of velocity always changes even though the speed is constant. Since the force is perpendicular to the direction of motion, the direction changes even though the speed remains constant.
When the acceleration and force are directed towards the center of the circle, they are called the centripetal acceleration and centripetal force. Centripetal means "center seeking". This is not to be confused with centrifugal which is a "dirty" word in physics and should not be used. There is no such thing as a centrifugal force - this is only what you feel due to inertia.
Showed using octagons that F ~ 1/R, and F ~ v^2.
The complete equation is F = m * v^2/R
In solving problems, you always choose one axis in the direction of the acceleration which is towards the center of the circle. Find the sum of the forces in the radial direction and, instead of setting it equal to m * a, draw a little lightning bolt, write the word "zap", and set the sum equal to m * v^2/R. We "Zap" it because we didn't actually derive the equation, just pulled it out of thin air.
Note that m * v^2/R has the units of mass * acceleration. It is the centripetal force. v^2/R is the centripetal acceleration.
There must always be something physical that you can name as the centripetal force. Never just write down a centripetal force without identifying what causes it.
Gave several examples of centripetal force and solved several problems using uniform circular motion.
Handed out RA 7.4 for homework due tomorrow.
Also handed out problem sheet on circular motion. The front side is for practice. The three problems on the back are for extra credit if handed in by Friday.
Uniform circular motion - Motion in a circle at constant (uniform) speed.
Showed using definition of acceleration, a = (vf-vi)/t and adding the vectors using the parallelogram rule that for uniform circular motion, the acceleration is directed towards the center of circle.
Since there is an acceleration directed towards the center of the circle, and F = m*a, there must be a force also directed towards the center of the circle. The acceleration is ALWAYS in the direction of the net force. There must be an acceleration since the direction of velocity always changes even though the speed is constant. Since the force is perpendicular to the direction of motion, the direction changes even though the speed remains constant.
When the acceleration and force are directed towards the center of the circle, they are called the centripetal acceleration and centripetal force. Centripetal means "center seeking". This is not to be confused with centrifugal which is a "dirty" word in physics and should not be used. There is no such thing as a centrifugal force - this is only what you feel due to inertia.
Showed using octagons that F ~ 1/R, and F ~ v^2.
The complete equation is F = m * v^2/R
In solving problems, you always choose one axis in the direction of the acceleration which is towards the center of the circle. Find the sum of the forces in the radial direction and, instead of setting it equal to m * a, draw a little lightning bolt, write the word "zap", and set the sum equal to m * v^2/R. We "Zap" it because we didn't actually derive the equation, just pulled it out of thin air.
Note that m * v^2/R has the units of mass * acceleration. It is the centripetal force. v^2/R is the centripetal acceleration.
There must always be something physical that you can name as the centripetal force. Never just write down a centripetal force without identifying what causes it.
Gave several examples of centripetal force and solved several problems using uniform circular motion.
Handed out RA 7.4 for homework due tomorrow.
Also handed out problem sheet on circular motion. The front side is for practice. The three problems on the back are for extra credit if handed in by Friday.
Friday, May 23, 2008
Friday, May 23, 2008
Handed back RA 7.2. Brandon worked out the final problem on the board.
Handed out worksheet on static equilibrium including problem solving strategy. Gave students time in class to work on the problems.
Finished class with short demos on center of mass:
balancing ruler, balancing bird, rolling on ramp, belt, finding center of mass of an object using a pin and string, unable to touch toes when standing against wall.
Mentioned how center of mass can be used with "wobble" of stars to find planets in other solar systems.
Students have circular motion lab due next Tuesday as well as try to finish torque problems.
Handed out worksheet on static equilibrium including problem solving strategy. Gave students time in class to work on the problems.
Finished class with short demos on center of mass:
balancing ruler, balancing bird, rolling on ramp, belt, finding center of mass of an object using a pin and string, unable to touch toes when standing against wall.
Mentioned how center of mass can be used with "wobble" of stars to find planets in other solar systems.
Students have circular motion lab due next Tuesday as well as try to finish torque problems.
Thursday, May 22, 2008
Thursday, May 22, 2008
While students who went the Physics Extravaganza filled out an evaluation form, other students unloaded equipment.
Introduced Circular Motion Lab. Explained frequency and period.
Students did Circular Motion Lab.
Lab write-up is due on Tuesday after the Memorial Day weekend.
Collected RA 7.2 and supplemental problems sheet on torque.
Handed out RA 7.3 due tomorrow.
Introduced Circular Motion Lab. Explained frequency and period.
Students did Circular Motion Lab.
Lab write-up is due on Tuesday after the Memorial Day weekend.
Collected RA 7.2 and supplemental problems sheet on torque.
Handed out RA 7.3 due tomorrow.
Wednesday, May 21, 2008
Showed all the demos for the Physics Extravaganza which is tonight at TuHS.
People practiced the demos for their booths.
Lots of people tried out the Van de Graaff.
People practiced the demos for their booths.
Lots of people tried out the Van de Graaff.
Tuesday, May 20, 2008
Tuesday, May 20, 2008
Went over RA 7.1
Talked about torque.
Demo opening door.
Finding lines of action and lever arms.
Ranking torques.
Demo with spool
Problem solving strategy for solving torque problems
Example problems on torque:
Seesaw
Canoe problem
Handed out RA 7.2, supplemental problems in torque - due tomorrow
Talked about torque.
Demo opening door.
Finding lines of action and lever arms.
Ranking torques.
Demo with spool
Problem solving strategy for solving torque problems
Example problems on torque:
Seesaw
Canoe problem
Handed out RA 7.2, supplemental problems in torque - due tomorrow
Thursday, May 15, 2008
Thursday, May 15, 2008
Went over RA 6.3, CD 6.1, CD 6.2
Most students did not look at WebAssign. Gave students 20 minutes working in pairs to do the problems.
Went over the questions from the end of the chapter.
Briefly described what to expect on tomorrow's test.
Most students did not look at WebAssign. Gave students 20 minutes working in pairs to do the problems.
Went over the questions from the end of the chapter.
Briefly described what to expect on tomorrow's test.
Wednesday, May 14, 2008
Wednesday, May 14, 2008
Last call for any Looney Tunes and Pulley Labs.
Went over Roller Coaster, Pulley Lab, and Looney Tunes Labs.
Quiz on momentum and energy.
Handed out CD 6.2 for homework.
Showed video, "How Things Go"
RA 6.3 is do tomorrow.
To prepare for Friday's test, students should complete CD 6.1, 6.2, and the WebAssign review of Hewitt Chapter 6 - energy.
Went over Roller Coaster, Pulley Lab, and Looney Tunes Labs.
Quiz on momentum and energy.
Handed out CD 6.2 for homework.
Showed video, "How Things Go"
RA 6.3 is do tomorrow.
To prepare for Friday's test, students should complete CD 6.1, 6.2, and the WebAssign review of Hewitt Chapter 6 - energy.
Tuesday, May 13, 2008
Tuesday, May 13, 2008
Collected Looney Tune and Pulley Labs.
Demo and calculations for ballistic pendulum using protractor. Requires both conservation of momentum and conservation of energy.
Students calculated the initial speed of the bullet as well as the percent energy that went into heat in the inelastic collision. Reviewed calculations in detail.
Quiz on finding speed and time for a ball dropped a given distance.
Quiz on block sliding down incline plane.
Handed out CD 6.2 on energy for homework.
Test on Friday
Demo and calculations for ballistic pendulum using protractor. Requires both conservation of momentum and conservation of energy.
Students calculated the initial speed of the bullet as well as the percent energy that went into heat in the inelastic collision. Reviewed calculations in detail.
Quiz on finding speed and time for a ball dropped a given distance.
Quiz on block sliding down incline plane.
Handed out CD 6.2 on energy for homework.
Test on Friday
Monday, May 12, 2008
Monday, May 12, 2008
Described problem on Roller Coaster Lab where students said power = force/time instead of power = energy/time
Went over energy problems with emphasis on energy balance equations.
Went over questions on WebAssign. Gave extension on WebAssign to Tuesday night.
Handed out RA 6.3 for students to work on in class and finish for homework.
Looney Tunes and Pulley Labs due tomorrow.
Went over energy problems with emphasis on energy balance equations.
Went over questions on WebAssign. Gave extension on WebAssign to Tuesday night.
Handed out RA 6.3 for students to work on in class and finish for homework.
Looney Tunes and Pulley Labs due tomorrow.
Friday, May 9, 2008
Friday, May 9, 2008
Day two of Looney Tune and Pulley labs. Write-ups due on Tuesday.
WebAssign due on Monday.
WebAssign due on Monday.
Thursday, May 8, 2008
Thursday, May 8, 2008
Pulley Lab and Looney Tune Lab - day 1
Went over what is required for Pulley Lab and Looney Tune Lab.
Both lab write-ups are due on Tuesday.
Went over what is required for Pulley Lab and Looney Tune Lab.
Both lab write-ups are due on Tuesday.
Wednesday, May 7, 2008
Wednesday, May 7, 2008
Review of energy
1. Kinetic energy - energy of motion = (1/2) * m * v^2
Did examples calculating KE
KE cannot be negative since m and v^2 are always positive.
If you double the mass, the KE doubles. Mass is proportional to KE. For the same velocity, a graph of KE vs m is a straight line through the origin with slope (1/2)v^2.
If you double the velocity, the KE increases by a factor of 4 (=2^2). Because velocity is squared, it has an even greater effect on the KE. If you make the velocity 3 times greater, the KE increases by a factor of 9. Did several examples including giving a KE of 3x10^6 J at 20 mph and finding KE at 40 mph, 120 mph.
A graph of KE vs v gives a parabola. A graph of KE vs v^2 gives a straight line through the origin with a slope of m/2
Slamming on brakes example. Energy balance equation is KE = work done by friction
(1/2) m v^2 = Ff * d
Since the friction force does not depend on the speed, if you double the speed, you increase the KE by a factor of 4 and increase the stopping distance by a factor of 4. Did several examples.
2. Gravitational potential energy = GPE = m*g*h
Did examples calculating GPE.
Graphs of GPE vs m and GPE vs h are straight lines through the origin.
Examples of choosing different locations for h = 0 (and thus GPE = 0).
GPE can be negative depending on the choice of h = 0. What is important is the difference in GPE between locations.
GPE does not depend on the path you took to get there.
3. Energy balance equations (equations for conservation of energy)
Energy you start with + energy you add = energy you end up with + places energy went
Energy balance equations:
Roller coaster lab
Introduced energy balance equation for Looney Tunes Lab
Showed energy balance equation for Looney Tunes Lab half-way down.
Energy balance equation for dropping an object with no air resistance.
Calculated speed of dropped object using energy. If you know the speed you can easily find the time.
Energy balance equation for an object that is thrown down.
4. Machines
Principle of machines is that work in = work out
Machines can change the force at the expense of distance. Machines do not "create" energy.
Showed examples using one and two strings to support and then lift a weight.
Introduced pulley lab ideas.
5. Handed out worksheet on energy problems. Gave students 15-20 minutes to work on it in class.
Roller Coaster Lab due tomorrow.
1. Kinetic energy - energy of motion = (1/2) * m * v^2
Did examples calculating KE
KE cannot be negative since m and v^2 are always positive.
If you double the mass, the KE doubles. Mass is proportional to KE. For the same velocity, a graph of KE vs m is a straight line through the origin with slope (1/2)v^2.
If you double the velocity, the KE increases by a factor of 4 (=2^2). Because velocity is squared, it has an even greater effect on the KE. If you make the velocity 3 times greater, the KE increases by a factor of 9. Did several examples including giving a KE of 3x10^6 J at 20 mph and finding KE at 40 mph, 120 mph.
A graph of KE vs v gives a parabola. A graph of KE vs v^2 gives a straight line through the origin with a slope of m/2
Slamming on brakes example. Energy balance equation is KE = work done by friction
(1/2) m v^2 = Ff * d
Since the friction force does not depend on the speed, if you double the speed, you increase the KE by a factor of 4 and increase the stopping distance by a factor of 4. Did several examples.
2. Gravitational potential energy = GPE = m*g*h
Did examples calculating GPE.
Graphs of GPE vs m and GPE vs h are straight lines through the origin.
Examples of choosing different locations for h = 0 (and thus GPE = 0).
GPE can be negative depending on the choice of h = 0. What is important is the difference in GPE between locations.
GPE does not depend on the path you took to get there.
3. Energy balance equations (equations for conservation of energy)
Energy you start with + energy you add = energy you end up with + places energy went
Energy balance equations:
Roller coaster lab
Introduced energy balance equation for Looney Tunes Lab
Showed energy balance equation for Looney Tunes Lab half-way down.
Energy balance equation for dropping an object with no air resistance.
Calculated speed of dropped object using energy. If you know the speed you can easily find the time.
Energy balance equation for an object that is thrown down.
4. Machines
Principle of machines is that work in = work out
Machines can change the force at the expense of distance. Machines do not "create" energy.
Showed examples using one and two strings to support and then lift a weight.
Introduced pulley lab ideas.
5. Handed out worksheet on energy problems. Gave students 15-20 minutes to work on it in class.
Roller Coaster Lab due tomorrow.
Tuesday, May 6, 2008
Monday, May 5, 2008
Monday, May 5, 2008
Introduction to Energy
Feynman block story
Around the class asking for forms of energy (places energy can hide)
Indicated the main forms of energy we will be concerned with: work, gravitational potential energy, kinetic energy, elastic potential energy, heat
Importance of energy is that if you add up all the places energy can hide before something happens and then do it after something happens, you will get the same number. Conservation of energy. The equation is the energy balance equation.
Showed equations for various forms of energy:
GPE = m*g*h = gravitational potential energy = energy of location or position
KE = 1/2 * m * v^2 = energy of motion
elastic PE = 1/2 * k * x^2 = energy stored in a stretched rubber band or spring with spring constant k and stretch x
Went over RA 6.1 on work
Discussed work in detail. Work = F * d where F is the component of force in the direction of motion. If the force is perpendicular to the direction of motion (velocity) no work is done by that force.
Compared work and impulse.
Did example of lifting block showing that work done is equal to the change in gravitational potential energy.
Showed some energy balance equations.
Handed out RA 6.2 due tomorrow.
If students scored less than 85 on the last test, the WebAssign assignment is required and due for tomorrow.
Feynman block story
Around the class asking for forms of energy (places energy can hide)
Indicated the main forms of energy we will be concerned with: work, gravitational potential energy, kinetic energy, elastic potential energy, heat
Importance of energy is that if you add up all the places energy can hide before something happens and then do it after something happens, you will get the same number. Conservation of energy. The equation is the energy balance equation.
Showed equations for various forms of energy:
GPE = m*g*h = gravitational potential energy = energy of location or position
KE = 1/2 * m * v^2 = energy of motion
elastic PE = 1/2 * k * x^2 = energy stored in a stretched rubber band or spring with spring constant k and stretch x
Went over RA 6.1 on work
Discussed work in detail. Work = F * d where F is the component of force in the direction of motion. If the force is perpendicular to the direction of motion (velocity) no work is done by that force.
Compared work and impulse.
Did example of lifting block showing that work done is equal to the change in gravitational potential energy.
Showed some energy balance equations.
Handed out RA 6.2 due tomorrow.
If students scored less than 85 on the last test, the WebAssign assignment is required and due for tomorrow.
Friday, May 2, 2008
Friday, May 2, 2008
Went over momentum test in some detail.
Showed video - Understanding Car Crashes.
Collected RA 6.1
Showed video - Understanding Car Crashes.
Collected RA 6.1
Thursday, May 1, 2008
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