19/04/10

MOMENT OF FORCE (TORQUE)

Elisa A. ValladolidErnesto Rondon High School

4th year High School

OBJECTIVE

Describe the moment of force in terms of it’s turning effects.

State the principle of moments for a body in equilibrium.

Apply principle of moments in everyday life.

Why moment of force/ torque?

Have you experienced playing seesaw?Can you play it alone?How does it turns?

Which is easiest way of opening the door?

(Demonstration; A. Opening the door by pulling/ pushing from the center . B. Opening the door through the knob.

Why?

(Share your answer with your seatmates)

( Explain why you choose A or B )

Situation A: A greater force is needed if

we open the door near the hinge.

Situation B: Less force or effort is

needed if we pull furthest from the hinge.

How does the door make it turn?

(the turning effect on the door is in the hinge, which a fixed

point also called the pivot and the turning effect of force

is also called Moment of Force /Torque)

What is the amount of moment of force/Torque?

Perform Activity no. ___ (Moment about a fixed pivot)

( Each group have a prepared set-up, and an activity sheet, they have to prepare their output in manila paper and present in class.)

Microsoft Office Word Document

Principle of moments

Pivot/ fulcrum

F

d

Again, turning effect of a force is called moment of force or torque.

Moment of a force = force x perpendicular

distance from the pivot = F x d SI unit is Newton-meter (N m)

Principle of moments

F F1 F2

d1 d2

Pivot/fulcrumAnticlockwise moment

Clockwise moment

Principle of moments: When an object is in

equilibrium, the sum of clockwise moments about any point is equal to the sum of anticlockwise moments about the same point.

Anticlockwise moment = Clockwise moment

Any Questions?

Evaluation

1. What is the name given to turning effect of a force about a pivot?

a. inertia b. moment c. pressure d. resultant

CORRECT!

Congratulations

The turning effect of force is called moment of force or torque.

2. It is better to use a longer spanner to undo a nut because

a. less force is exerted be the user.

b. less moment is applied on the spanner.

c. less friction is present. d. greater inertia is present.

CORRECT!

Congratulations

Moment of force = force x distance with a greater distance it lessen the moment.

3. A door requires a minimum moment of 32.5 N m to open it,

hingehandle

X

What is the minimum distance between the handle and the hinges, if the door is to be pulled with a force on the handle not greater than 50 N?

a. 0.33 m b. 0.25 m c. 0.65 m d. 1.54 m

CORRECT!

Congratulations

Moment of force = F x d 32.5 = 50 N x d 32.5 = d 50 0.65 m = d

4. The diagram below shows a light rod with weights hanging from it. The system is not in equilibrium. What is the moment required to bring the system into equilibrium?

5n

4n

0.8m 1.5 m

moment direction a. 2 Nm clockwise

b. 6 Nm anticlockwise

c. 4 Nm clockwise d. 2 Nm anticlockwise

CORRECT!

Congratulations

Anticlockwise moment = clockwise moment F x d = F x d 5 N x .8 m = 4 N x 1.5 m

4Nm= 6 NmTo make it in equilibrium need 2nm from theAnticlockwise moment.

5. A light rod is in equilibrium under the action of the force as shown below. What is the magnitude of the force F?

20 N F 12 N

2m 1m 1 m

a. 28 N b. 8 N c. 16 N d. 4 N

CORRECT!

Congratulations

Anticlockwise moment = clockwise moment F3 x d3 = F1 x d1 + F2 x d2

20 N x 2m = F x 1 m + 12 N x 1 m 40 Nm = 1 F + 12 Nm 40 Nm -12 Nm = 1 F 28 Nm = 1 F 1m 1 28 N = F

Assignment

A. What is the center of gravity?

B. How is the center of gravity related to stability?

Sorry!

That was the wrong answer