Forces

Question 1

4 contact forces

Answer 1

• friction
• normal contact/ reaction force
• air resistance
• tension

Question 2

3 non contact forces

Answer 2

• weight/ gravitational
• magnetic
• electrostatic

Question 3

what is a force?

Answer 3

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

Question 4

what is weight?

Answer 4

The force acting on an object due to the pull of gravity from a massive object like a planet. The force acts towards the centre of the planet and is measured in newtons (N).

Question 5

what does the magnitude of weight depend on?

Answer 5

the gravitational field strength

Question 6

where does the weight of an object act?

Answer 6

at a single point that is referred to as the centre of mass

Question 7

define resultant force

Answer 7

The single force that could replace all the forces acting on an object (when several forces act on an object), found by adding these together. If all the forces are balanced, the resultant force is zero.

Question 8

what does a free body diagram depict?

Answer 8

The object or ‘body’ is usually shown as a box or a dot. The forces are shown as thin arrows pointing away from the centre of the box or dot.

Question 9

what does a vector diagram depict?

Answer 9

• an x and y axis with arrows in the directions of the two forces
• a simple scale converting cm to the number of newtons on each axis
• diagonal line with arrow going to the top of both scales
• can draw a line at the end to form a right angle triangle

Question 10

what is one joule equal to?

Answer 10

One joule of work is done (or one joule of energy is transferred) when a force of one newton causes a body to move through a distance of one metre.

Question 11

what is a joule?

Answer 11

when a force of one newton causes a body to move through a distance of one metre.

Question 12

relationship between joules and newton-metres

Answer 12

• work done can also be measured in newton-metres (Nm):
• 1 J = 1 Nm
• dont confuse newton-metres with newton meters

Question 13

why does work done against the frictional forces acting on an object cause a rise in the temperature of the object?

Answer 13

• Work is done against
  friction which causes heating of the two surfaces - so the internal (thermal) energy of the surfaces increases.
• energy is dissipated when two surfaces rub together.

Question 14

give an example of bending and describe the forces involved in it

Answer 14

• Bend an object’s ends past each other
• eg when an archer pulls an arrow back against a bow.
• balanced forces ancting both ways on one end
• force pushing down on the other end

Question 15

give an example of stretching and describe the forces involved in it

Answer 15

• Pull an object’s ends apart
• eg when a rubber band is stretched.
• forces acting in opposite directions pointing away from the object

Question 16

give an example of compressing and describe the forces involved in it

Answer 16

• Push an object’s ends together
• eg when an empty drinks can is squashed.
• forces acting in opposite directions pointing in to the object

Question 17

why does more than one force have to be applied when changing the shape of a stationary object?

Answer 17

because a single force would simply cause the object to move in the direction in which the force were to be applied

Question 18

define elastic deformation

Answer 18

it is reversed when the force is removed

Question 19

define inelastic deformation

Answer 19

is not fully reversed when the force is removed - there is a permanent change in shape

Question 20

what happens when a material goes past its elastic limit?

Answer 20

Once a material has gone past its elastic limit, its deformation is said to be inelastic.
In this instance, the relationship between force and extension changes from being linear, or directly proportional, to being non-linear.

Question 21

how is linear and non linear extension shown on a graph

Answer 21

• Linear extension and elastic deformation can be seen below the limit of proportionality.
• Non-linear extension and
  inelastic deformation can be seen above the limit of proportionality.
• The limit of proportionality is also described as the ‘elastic limit’.
• The gradient of a force-extension graph before the limit of proportionality is equal to the spring constant and goes up in a straight diagonal line
• once this line becomes more horizontal, the extension is non-linear