AP Physics Torque Turning or twisting effects due to a force The product of force and perpendicular distance from pivot point aka level arm Can produce ID: 783369
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Slide1
Torque & Equilibrium
AP Physics
Slide2Torque (
)
Turning or twisting effects due to a force
The product of
force
and
perpendicular distance
from pivot point
(a.k.a.
level
arm
)
Can produce
changes in
rotation
End Slide
Pivot Point
Slide3Torque
(
) Examples
A bolt on a car engine needs to be tightened with a torque of . You use a 25-cm long wrench and pull on the end of the wrench at an angle of from the perpendicular. How long is the lever arm, and how much force do you have to exert?
End Slide
Slide4Torque
(
) Examples
If a torque of is required and the largest force that can be exerted by you is , what is the length of the lever arm that must be used?
You have a 23.4-cm long wrench. A job requires a torque of
, and you can exert a force of
. What is the smallest angle, with respect to the wrench, at which the force can be exerted?
You stand on the pedal of a bicycle. If you have a mass of
, the pedal makes an angle of
above the horizontal, and the pedal is
from the center of the chain ring, how much torque would you exert at this moment?
Slide5Torque
(
) Examples
You stand on the pedal of a bicycle. If you have a mass of , the pedal makes an angle of above the horizontal, and the pedal is from the center of the chain ring, how much torque would you exert at this moment?
End Slide
Slide6Equilibrium
Conditions of Equilibrium:
Counter-Clockwise = Positive
Clockwise = Negative
In the diagram to the right, with how much force is the fulcrum pushing up?What is ?
End Slide
Slide7Equilibrium
Can I choose a different pivot point?
I don’t want to system to rotate about
ANY
point, right?What if I choose here, can I still determine ?
End Slide
Slide8Equilibrium Examples
Carl, whose mass is 43 kg, sits 1.8 m from the center of a seesaw. Steve, whose mass is 52 kg, wants to balance Carl. How far from the center of the seesaw should Steve sit?
End Slide
Slide9Car on a Bridge
A bridge with an evenly distributed mass of 1200 kg spans a gap of 86 meters. A car of mass 720 kg is 25 m onto the bridge from the right. How much force is holding up each end of the bridge?
Pivot Point
End Slide
Slide10Car on a Bridge
The same bridge with mass of 1200 kg spanning an 86-meter gap has a 720-kg car that is now at 68 m from the right. How much force is holding up each end of the bridge this time?
Pivot Point
End Slide
Slide11Tilt the Box
Consider the rectangular block of mass 27 kg, height 1.1 m, and length
0.8
m. A force F is applied horizontally at the upper edge.
A) What minimum force is required to start to tip the block? The acceleration of gravity is 9.8 m/s2. Answer in units of N.
Pivot Point
Because the box will be tilted, all of the Normal Force will be applied at the corner rather than evenly distributed on the bottom.
Normal Force and Force of Friction are being applied at the pivot point; thus, no torque.
End Slide
Slide12Tilt the Box
Consider the rectangular block of mass 27 kg, height 1.1 m, and length
0.8
m. A force F is applied horizontally at the upper edge.
B) What minimum coefficient of static friction is required for the block to tip with the application of a force of this magnitude?
Free-Body
Diagram
Pivot Point
End Slide
Slide13Jill Climbs a Ladder
Consider a uniform ladder of weight 250 N and length 10 m leaning against a smooth, vertical wall and is resting on a floor with friction. Jill weighs 600 N and is standing on the ladder 2 m from the bottom. The foot of the ladder is 0.8 m from the base of the wall.
A) What
is the Normal force on the ladder exert by the ground?
Free-Body
Diagram
What’s the system?
The ladder
Slide14Jill Climbs a Ladder
Consider a uniform ladder of weight 250 N and length 10 m leaning against a smooth, vertical wall and is resting on a floor with friction. Jill weighs 600 N and is standing on the ladder 2 m from the bottom. The foot of the ladder is 0.8 m from the base of the wall.
A) What
is the Normal force on the ladder exert by the ground?
Free-BodyDiagram
End Slide
Slide15Jill Climbs a Ladder
Consider a uniform ladder of weight 250 N and length 10 m leaning against a smooth, vertical wall and is resting on a floor with friction. Jill weighs 600 N and is standing on the ladder 2 m from the bottom. The foot of the ladder is 0.8 m from the base of the wall.
B)
What is the force exerted by the wall?
Pivot Point
No Torque
No Torque
Slide16Jill Climbs a Ladder
Consider a uniform ladder of weight 250 N and length 10 m leaning against a smooth, vertical wall and is resting on a floor with friction. Jill weighs 600 N and is standing on the ladder 2 m from the bottom. The foot of the ladder is 0.8 m from the base of the wall.
End Slide
B)
What is the force exerted by the wall?
Slide17Jill Climbs a Ladder
Consider a uniform ladder of weight 250 N and length 10 m leaning against a smooth, vertical wall and is resting on a floor with friction. Jill weighs 600 N and is standing on the ladder 2 m from the bottom. The foot of the ladder is 0.8 m from the base of the wall.
End Slide
C) What is the minimum coefficient of static friction between the ladder
and the ground?