*Turning Effect of Force

Shie Yu Hao (22)Per Sheng Xiang (19)

Force A

-A smaller force is needed if

applied nearer to hinge

*Small recap

Pivot

Hinge

Force B -A larger force is needed if applied further to hinge

2 factors which the door turns depends: • Magnitude (Amount) of force• Distance of the force applied from the pivot

*Now, you would learn how to calculate the force that has been exerted!

Measure the turning effect

*Moment of a force*Definition:

The moment of a force (torque) is the product of the force and the perpendicular distance from the pivot to the line of action of the force.

Moment of Force= FxD where

F is the force and

D is the perpendicular distance from the pivot

*Moment of Force can move anti-clockwise or clockwise.

Hinge

* Force A

* -A smaller force is needed if

applied nearer to hinge

Force B -A larger force is needed if applied further to hinge

Weight Z= 5N

A B

C- 10cm

D- 30cm

Find the moment of force applied at A and B.

Perpendicular to pivot

Perpendicular distance of C = 10cm= 0.1m

Moment of Weight Z about the pivot(A)

= Z x C

= 5N (Weight) x C (Distance)

=5x0.1

=o.5N m

The force needed to lift the weight Z is 0.5N m.

Weight Z= 5N

C- 10cm

A Similarly,

Perpendicular distance of C+D = 40cm= 0.4m

Moment of Weight Z about the pivot(A)

= Z x C

= 5N (Weight) x C+D (Distance)

=5x0.4

=2.0N m

The force needed to lift the weight Z is 2.0N m.

Weight Z= 5N

C+D- 10cm+30cm=40cm

B

*Equilibrium

d d

How did the objects balance?The force acting on the two objects would be the

same, right?

Mg Sg

d d

Remember, Moment of Force can move anti-clockwise or clockwise. So,

Mg Sg

Anti-clockwise moment= Mg x d Clockwise moment= Sg x d

Since they are equal:

Mg x d= Sg x d M= S

Mg= Mass x gravitational force Sg= Total standard masses x gravitational force

In simpler words, The above equation derived us why the beam is balanced.

*Principle of Moments

*What happens if the distance of your 2 objects are different away from the pivot?

*Can we still calculate the force exerted?

*OF COURSE! WE WOULD USE PRINCIPLE OF MOMENTS!

*Principle of Moments

*From the above equation:

Mg x d= Sg x d

We know that the clockwise moment of force is the same as the anti-clockwise moment of force in an equilibrium

Let’s do an experiment to prove it!

d1 d2

W1- 0.5N

W2- 0.4N

We would change the distance of d1 and d2 for every experiment we do. Observe the results later.

*Optional

*Ask the class to try out the experiment themselves!

W1/N d1/cm Anti-clockwise moment W1 x d1/N cm

W2/N d2/cm Clockwise moment W2 x d2/N cm

0.5

0.5

0.5

0.5

0.4

0.4

0.4

0.4

*Principle of Moments

W1/N d1/cm Anti-clockwise moment W1 x d1/N cm

W2/N d2/cm Clockwise moment W2 x d2/N cm

0.5

0.5

0.5

0.5

32

45

40

36

16

9

20

18

0.4

0.4

0.4

0.4

40

22.5

50

30

16

9

20

18

From the above experiment,

We know that anti-clockwise moments of force will be the same as clockwise moments of force when there are balanced.

Now, how do we find the distance if we are given the moments of force and weight?

Just reverse all the steps!

Force/ Weight = Distance