Motion Revision

Vectors must have a direction and magnitude

Scalars are of how much there is

Resultant forces show the overall effect of multiple forces

If an object is already moving and the forces are balanced, it will keep moving, but it will be at constant speed.

The weight of an object acts on a single point- the centre of mass

• a useful concept for designers and engineers

Suspended equilibrium

If you suspend an object and then realease it, it will eventually come to rest with its centre of mass directly below the point of suspension.

Symmetrical objects

The centre of mass for a symmetrical object lies along the axis of symmetry

Unsymmetrical objects

1) Hang the shape from one of the holes

2) Use a plumb line (weight on the end of string) to draw a vertical line on the shape from the rod

3) Repeat the procedure, hanging the shape from a different hole

• Gradient of the line represents speed
• The steeper the gradient, the faster the object is moving
• A gradient of 0 means the object is stationary

Constant speed equation:

Speed= distance travelled / time taken

v=s/t

Velocity

• It is the speed in a given direction

Two moving objects can have the same speed but different velocities

Acceleration

a= change in v / t

Horizontal line= zero acceleration ( at a constant speed)

The gradient of the line represents acceleration

Braking

• braking reduces the velocity of vehicle

the area under the line on a velocity-time graph represents distance travelled in a given direction (displacement) ---> a vector

Resultant force = mass x acceleration

F= m x a

Newton's Second Law

Acceleration of an object is:

• proportional to the resultant force on the object
• Inversely proportional to the mass of the object

1N of the resultant force gives a 1KG mass an acceleration of 1M/S2