Turning Effects of Forces | O Levels

 

Turning Effects of Forces

O level by Owais Khan

Objects fixed in such a way that they could move about the point are said to experience a turning effect.

The position at which they are fixed so they can move around, such a position is called a pivot.

Pivot can also be a position or point at which an object is placed in such way that object can turn around that position. Example: A position where a bottle opener is placed.

Examples of Turning Effects:

·         Opening or closing a door

·         Movement of a rotating fan

·         Movement of a human arm

·         Lifting a weight with a lever

Moments:

It is the product of force and perpendicular distance from the line of action of the force till the pivot. Moment causes a turning effects.

     Pivot

Moment = F x d

SI unit of moment = Nm

                                                    

      

Where F = force in Newton

        d = Perpendicular distance from                                  

                                                                                                                d 

                    line of action in meter (m).                                                                  F                     

                                                                                                  

Principal of moments:

For a system to be in equilibrium, the sum of the clockwise moment must be equal to the sum of anti-clockwise moment.

                          Sum of anti-clockwise moment = Sum of clockwise moment

W₁d₁=W₂d₂ 

Sample Question:

Find the weight of the computer if the tabletop is in equilibrium:

Answer

Sum of clockwise moment = Sum of anti-clockwise moment

0.25m x W = 62.5N x 0.8m

W = 62.5N x 0.8m

              0.25m

W =   50

       0.25

W = 200N Ans.

Determination of the center of mass of a plain lamina:

      1)      First make four holes at the different edges of plain lamina,

2)      Set up a retort stand with a cork and pin it as shown in the figure

3)      Tie hole A with a thread on the pin and let the lamina move freely until it stops.

4)      Attach a plumbline, which is a thread attach to a mass on one end, to the pin.

5)      Mark the dot on the other end of A corresponding to the plumbline, and join this dot to A with a line.

6)      Repeat this with B,C and D

7)      The point of intersection of four lines is the center of mass of the lamina 

Stability of an object:

Where A = Base Area

And      h = Height    

Case1:

If     A₁ = A₂

And h₁ > h2

Then 2 is more stable then 1

Because the center of gravity of 2 is comparatively lower than 1

Case 2:

If h₁ = h₂

And A₁ > A₂

Then 1 is more stable then 2

Because the base area of 1 is comparatively greater then 2

                                                                                                                    

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