The turning effect of a force is called its moment. The size of the momen is shown in the equation:
moment = force (N) x perpendicular distace from the line of action of force to the pivot (m)
To increase the moment:
- increase the force or,
- increase the distance to the pivot
When using a lever the force we are trying to move is called the load and the force applied to the lever is the effort.
Centre of Mass:
The centre of mass of an object is the point where its mass can be thought to be concentrated.
You can find the centre of mass of a thin object by:
1) suspend the thin sheet from a pin held in a clamp stand
2) hand the plumbline from the same pin
3) mark the line of the plumbline against the sheet
4) hang the sheet from the pin at another point and repeat the procedure
5) the centre of mass is where the two lines cross
Moments in Balance and Stability:
We can take moments about any point on an object and will find the total clockwise and total anti-clockwise moments are equal. This shows it is in equilibrium.
If the line of action of the weight lies outside the base of an object, there will be a resultant moment and the object will tend to topple over.
The stability of an object is increased by having a wider base and lower centre of mass.
Pressure is given by the equation:
Pressure (N/m2) = force (N) / the cross section at right angles to the direction of force (m2)
The pressure in a liquid is transmitted equally in all directions. The force exerted at one point will be transmitted to other points in the liquid.
The force exerted by a hydraulic pressure system depends on:
- the force exerted on the system
- the area of the cylinder where the force acts
- the area of the cylinder that exerts the force.
When an object moves in a circle it is continuously changing direction and therefore changing velocity. This is called centripetal acceleration.
An object only accelerates when a resultant force acts on it. This is called the centripetal force and always acts towards the centre of the circle. If the centripetal force stops acting, the object will continue to move in a straight line at a tangent to the circle.
The centripetal force increases as:
- the mass of the object increases
- the speed of the object increases
- the radius of the circle decreases
A pendulum moves to and fro along the same line, this is called oscillating motion.
The pendulum consists of a bob suspended on string. The bob oscillates back and forth through the equilibrium position. The amplitute is the distance from the equilibrium position to the highest position on either side.
The time period depends on the length only and increases and length increases.