5: Forces

Question 1

What is the difference between a scalar and a vector?

Answer 1

Scalar quantities have magnitude only.

Vector quantities have magnitude and an associated direction.

Question 2

What is the difference between a contact and a non-contact force?

Answer 2

Contact forces: the objects are physically touching
- Friction
- Air resistance
- Tension
- Normal contact

Non-contact forces: the objects are physically separated
- Electrostatic
- Weight
- Magnetism

Question 3

What is the equation for calculating weight?

Answer 3

W = mg

W: weight (newtons, N)

m: mass (kilograms, kg)

g: gravitational field strength (Newtons per kilogram, N/kg)

Question 4

What is the resultant force?

Answer 4

A number of forces acting on an object may be replaced by a force that has the same effect as all the original forces acting on together. This single force is called the resultant force.

A single force can be resolved into two components acting at right angles to each other. These two component forces together have the same effect as a single force.

Question 5

What is the equation for calculating mechanical work done?

Answer 5

W = Fs

W: work done (joules, J)

F: force (newtons, N)

s: distance (metres, m)

Question 6

What is the difference between plastic and elastic deformation.

Answer 6

If the object, after being deformed, does not return to its original shape, is plastic deformation. If the object returns to its original shape, it is elastic deformation.

Question 7

State Hooke’s law

Answer 7

The extension of an elastic object, such as a spring, is directly proportional to the force applied, providing that the limit of proportionality is not exceeded.

F = ke

F: force (newtons, N)

k: spring constant (newtons per metre, N/m)

e: extension: (metres, m)

Question 8

What is the equation for calculating elastic potential energy?

Answer 8

E = 1/2ke²

E: elastic potential energy (joules, J)

k: spring constant (newtons per metre, N/m)

e: extension (metres, m)

Question 9

What is the difference between distance and displacement?

Answer 9

Distance is how far an object moves. It does not involve direction. Distance is a scalar quantity.

Displacement involves both the distance the object moves and the direction of the straight line. Displacement is a vector quantity.

Question 10

What is the equation for calculating distance travelled from speed?

Answer 10

s = vt

s: distance (metres, m)

v: speed (metres per second, m/s)

t: time (seconds, s)