Turning forces and Centre of Gravity Chapter 43

Turning forces and Centre of Gravity Chapter 43

The Turning effect of a force The turning effect of a force can be increased in 2 ways. 1. 2. Increasing the size of the force itself. By increasing the distance of the applied force to the fulcrum. • The point about which the object turns is referred to as the fulcrum.

Moment of a force • The moment of the force or the turning effect of the force. • Moment of a force = (Force) x (perpendicular distance from the force to the fulcrum)

A Lever used to turn a tap

What is the moment of the force(turning effect) that is being exerted in the following diagram? Answer: Moment = Force x distance from fulcrum 40 N x 0. 2 m =8 Nm

Levers • A lever is a rigid body which is free to turn about a fixed point called the fulcrum. Examples of Levers: A door, wheelbarrow, crowbar, see-saw,

Here are 3 examples of lever’s. In each case identify which is the effort, load and fulcrum

Answer

Levers • Levers can be used to exert a large force over a small distance at one end by exerting only a small force over a greater distance at the other

The law of the lever The Law of the lever states that when a lever is balanced , the sum of the clockwise moments are equal to the anti-clockwise moment.

Balancing a Meter Stick

Is This Meter Stick Balanced?

Is this lever balanced? Left Hand side Moment = Force x Distance 1 N x 40 cm = 40 Ncm Right Hand Side Moment = Force x Distance = 2 N X 25 cm = 50 Ncm Therefore The Lever is not Balanced. Where must the 2 N weight be placed to have a balanced meter stick?

What is the value of y?

Where must the 32 N weight be hung to balance the meter stick?

Find the Weight of the stone

Question: Calculate where the 5 N weight must be placed so as to have a balanced lever?

Left Hand Side Right hand side 5 x y = 5 y 8 x 12 = 96 13 x 7 = 91 6 x 18 = 108 2 x 46 = 92 ------------Total 91 + 108 + 92 =291 -----------Total 96 + 5 Y 5 Y = 291 - 96 5 Y = 195 Y = 39 Therefore the 5 N weight is at the 11 cm mark

Center of Gravity. • The center of gravity of an object is the point through which the weight of an object appears to act.

To find the center of gravity of a sheet of cardboard:

Equilibrium • A body is in stable equilibrium if, when slightly moved or tilted, its center of gravity rises. • A body is in unstable equilibrium if, when slightly moved or tilted, its center of gravity falls. • A body is in neutral equilibrium if, when slightly moved or tilted, its center of gravity neither rises or falls.

Types of Equilibrium

Equilibrium

Equilibrium

• Objects in stable equilibrium will have a wide base and a low center of gravity. In designing a bus, for example, a low center of gravity makes a bus more stable and less likely to topple over.

Unstable equilibrium