5.1 Forces

Question 1

Scalar and vector quantities

Answer 1

Scalars are quantities that have only a magnitude.
Examples include distance, time, speed, mass.

Vector quantities have both a magnitude and a direction.
Examples include displacement, velocity, acceleration.

Question 2

Forces

Answer 2

A force is a push or a pull that acts on an object when it interacts with another object.
When an object experiences a force it can deform or accelerate.

Question 3

Contact forces

Answer 3

Contact forces happen when two objects are physically touching.
Friction - sliding across a surface.
Lift - upward force on a wing.
Thrust - propulsive force of an engine.
Up thrust - upwards force when an object is in a fluid
Drag - acts against objects moving through a fluid.
Tension - is described as a pulling force transmitted by a string or similar object.
Normal contact force - push or a pull.

Question 4

Non - contact forces

Answer 4

Non-contact forces happen when objects are separated (not touching).
Weight - force due to gravity.
Magnetic - force between magnetic objects.
Electrostatic - force between charged objects.

Question 5

Gravity

Answer 5

Weight is the force acting on an object due to gravity.
Weight = mass x gravitational field strength
W = mg

Question 6

Mass

Answer 6

The mass of an object is a measure of the amount of matter it contains. The mass of an object is constant.

Question 7

Centre of mass

Answer 7

The centre of mass is the point through which an object’s weight appears to act.
An object will fall over if its centre of mass is outside its base.
An object will fall off a surface if its centre of mass isn’t over the surface.

Question 8

Resultant force

Answer 8

A resultant (net) force is a single force that describes all of the forces operating on a body.
This single resultant force determines:
The direction in which the object will move as a result of all of the forces.
The magnitude of the final force experienced by the object.

Question 9

Balanced and unbalanced forces

Answer 9

Balanced forces mean that the forces have combined in such a way that they cancel each other out and no resultant force acts on the body.
Unbalanced forces mean that the forces have combined in such a way that they do not cancel out completely and there is a resultant force on the object.