scalars and vectors

5.1.1 Scalar and vector quantities Revised?

Scalar quantities have magnitude only.

Vector quantities have magnitude and an associated direction.

A vector quantity may be represented by an arrow. The length of the arrow

represents the magnitude, and the direction of the arrow the direction of the

vector quantity.

5.1.2 Contact and non-contact forces Revised?

A force is a push or pull that acts on an object due to the interaction with another

object. All forces between objects are either:

 contact forces – the objects are physically touching

 non-contact forces – the objects are physically separated.

Examples of contact forces include friction, air resistance, tension and normal

contact force.

Examples of non-contact forces are gravitational force, electrostatic force and

magnetic force.

Force is a vector quantity.

You should be able to describe the interaction between pairs of objects which

produce a force on each object. The forces to be represented as vectors.

5.1.3 Gravity Revised?

Weight is the force acting on an object due to gravity. The force of gravity close to

the Earth is due to the gravitational field around the Earth.

The weight of an object depends on the gravitational field strength at the point

where the object is.

The weight of an object can be calculated using the equation:

weight = mass × gravitational field strength

W = mg

weight, W, in newtons, N

mass, m, in kilograms, kg

gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation

the value of the gravitational field strength (g) will be given.)

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The weight of an object may be considered to act at a single point referred to as

the object’s ‘centre of mass’.

The weight of an object and the mass of an object are directly proportional.

Weight is measured using a calibrated spring-balance (a newtonmeter).

5.1.4 Resultant forces Revised?

A number of forces acting on an object may be replaced by a single force that has

the same effect as all the original forces acting together. This single force is called

the resultant force.

You should be able to calculate the resultant of two forces that act in a straight

line.

You should be able to describe examples of the forces acting on an isolated object

or system.

You should be able to use free body diagrams to describe qualitatively examples

where several forces lead to a resultant force on an object, including balanced

forces when the resultant force is zero.

A single force can be resolved into two components acting at right angles to each

other. The two component forces together have the same effect as the single force.

You should be able to use vector diagrams to illustrate resolution of forces,

equilibrium situations and determine the resultant of two forces, to include both

magnitude and direction (scale drawings only).