Intro to torque

Forces in balance

We have talked about forces in balance all semester. When forces are in balance, the acceleration is 0.

Multiple Choice

If P are both forces pressing down on this beam, does this beam seem balanced?

• Yes, there's no reason anything would accelerate in any direction

• Maybe
• Not sure
• No

Multiple Choice

If the gray pedestals are removed would this system be in balance in the X and Y directions?

• yes, because there is a normal force that is equal and opposite in the y direction, and nothing is happening in the x direction

• no because it would rotate

• no because there would be an extra force at the end

• yes because of the centripetal force

Multiple Choice

If the gray pedestals are removed, this does have balance in X and Y but is there anything unbalanced?

• yes, because there is a normal force that is equal and opposite in the y direction, and nothing is happening in the x direction

• no because it would rotate

• yes because it would rotate

• yes because of the centripetal force

Multiple Choice

Where would you have to move the right weight to balance things?

• 6

• 7

• 8

• 9

You probably realized the previous example isn't balanced. This means there is an acceleration, but it isn't in the X or Y direction, it is a twisting force. This is called torque

Torque is a force that causes an acceleration either clockwise or counter clockwise.

Calculating torque

This is a two step process
1) Determine the point of rotation, this can actually be any point but pick one that makes sense.
2) multiply the distance between the point of rotation and the perpendicular component of the force.
The distance between the force location and the point of rotation is called the moment arm.
Two get the perpendicular component we sometimes have to multiple by sin or cos

Multiple Choice

Torque is the product of a force exerted on an object times the lever arm.

• True 
• False

Multiple Choice

What is the Unit for Torque

• Nm
• N
• W
• J

Multiple Choice

What is the torque relative to the center due to the weight on the left? (don't forget to multiply m by g)

• 1400 Nm counter clockwise

• 140N

• 40 N

• 400 Nm clockwise

Multiple Choice

What is the formula for calculating torque ( $$\tau$$ )?

• $$\tau=F+d\sin\Delta$$

• $$\tau=\frac{F}{d\sin\theta}$$

• $$\tau=Fd\sin\theta$$

• $$\tau=\frac{d\sin\theta}{F}$$

If the torque is balanced, there is no rotational force

Multiple Choice

The torque on the right is about 1400 Nm counter clockwise what would the weight on the right side have to be to balance the torque?

• 40 kg

• 60 kg

• 70 kg

• 90

Multiple Choice

If a torque of 60 Nm is applied to a wrench with a length of 0.5 m, what is the force applied at the end of the wrench?

• 30 N

• 120 N

• 300 N

• 600 N

Multiple Choice

When an object is experiencing a net torque

• it is in dynamic equilibrium.
• it is in static equilibrium.
• it is rotating.
• it is translating.

Multiple Choice

Find the magnitude of the torque produced by a 5.0 N force applied to a door at a perpendicular distance of 65 cm from the hinge.

• 75 Nm
• 3.25 Nm
• 6.3 Nm
• 8.75 Nm

Multiple Choice

What is the weight of the package?

• 5 N
• 10 N
• 15 N
• 20 N