December 1AP Physics

Introducing….TORQUE

Last Day for Late Work…

Friday, December 11

In:

How do things start to turn in a circle?

Objective:

To explore the concept of Torque and rotational equilibrium.

Exploration: Torque

Problem: How can you balance two unequal masses?

What did you do? What did you notice?

What did you notice?

Conclusion:

• What can we say about torque?

Torque

Τ= rFsinθDistance times Force perpendicular

Right hand rule

• Extend hand in the direction of r

• Curl fingers in direction of force

• Thumb toward you, positive torque (counterclockwise)

• Thumb away, negative torque (clockwise)

For Equilibrium (balance)

• The sum of all torques around any point have to add up to zero.

Most doorknobs are placed on the side of the door opposite the hinges instead of in the center of the door.

• Why is this so?

• If a torque of ½ Nm is required

to open a door, how much force

must be exerted on a door knob

.76 m from the hinges compared

to a door knob in the middle of

the door, .38 m from the hinges?

Cilla is working out in the gym

with a 2 kg mass that she holds in

one hand and gradually lifts up

and down.

Will Cilla find in easier to lift the mass if she pivots her arm at the shoulder or at the elbow?

If Cilla’s arm is .60 m long from her sholder to her palm and .28 m long from her elbow to her palm, how much torque must she produce in each case to lift he weight?

Leif and Joan are rearranging the heights of their book shelves and they remove one of the 2 kg .60 m long shelves by each holding one end. A 5 kg stack of books is piled up on the shelf .2 m from Leif. How much force must leif and joan each exert to hold the shelf level?

Out:

How far from the axis of a teeter-totter would a 400 N person have to be to balance a 800 N person who is 2 meters from the axis?