Forces

Question 1

what is a force?

Answer 1

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

Question 2

Newton meter is used to measure…

Answer 2

forces

Question 3

what is force measured in?

Answer 3

Newtons (N)

Question 4

What are the 2 main categories of force?

Answer 4

contact force and non-contact force

contact force - two objects must be touching each other to exert a force
non-contact force - two objects do not need to be touching to exert a force

Question 5

what are force arrows/vectors?

Answer 5

used to represent the force(s) acting on an object in a diagram

Question 6

The length of a force arrow shows the…

Answer 6

magnitude of the force (size of the force)

The longer its length, the larger the magnitude of the force

36N is a larger force size than 23N.

Question 7

Gravitational force (gravity)…

Answer 7

a non-contact force which pulls two objects towards each other. It never pushes them apart

Gravitational force is experienced by a mass when it is sufficiently close to another mass.

In the diagram, Earth pulls the satellite and the satellite pulls Earth. The forces are equal in size and opposite in direction.

Question 8

Friction…

Answer 8

a contact force that acts between two touching surfaces and prevents or resists them moving against each other (Friction goes against or pulls the opposite way on depending where an object is moving towards)

When two objects slide past each other they experience friction

Question 9

Air resistance…

Answer 9

a contact force which is a resistive force that acts against objects that are moving through the air
this force acts against the direction of movement.

The faster the object is travelling the greater the air resistance.

TYPE OF FRICTION

Question 10

Water resistance…

Answer 10

a contact force which acts against an object moving in water towards a direction

TYPE OF FRICTION

Question 11

Upthrust…

Answer 11

a contact force which is an upwards force that acts on an object when it is in a fluid (a liquid or gas)

Question 12

Normal Reaction…

Answer 12

a contact force and is when an object pushes on a surface like a table, wall or the ground, the surface pushes back on the object with a balancing force.

The normal reaction force always acts at right angles to the surface.

Question 13

Tension…

Answer 13

a contact force which is a pulling force exerted on an object by a string, rope or rod

Question 14

Thrust…

Answer 14

a contact force which is a driving force exerted by an engine to make an object move.

Question 15

Electro-static force…

Answer 15

a non-contact force which is experienced by a charged particle in an electric field.

This force can be either attractive or repulsive.

Question 16

Magnetic force…

Answer 16

a non-contact which is experienced by a magnet or a magnetic material, eg iron, when placed in a magnetic field.

This force can pull the two objects together or push them apart.

Question 17

what is mass and what is it measured in?

Answer 17

amount of matter an object has and is measured in kg.
It is almost a count of all the particles in an object. That’s why it doesn’t change if you take it from the Earth to the Moon

Question 18

what is weight and what is it measured in?

Answer 18

the force that acts on mass due to gravity and is therefore measured in newtons (N)
force pulling an object down to the ground (mass) caused by gravity

Not the same as mass and is also referred to as the total force produced by gravity.

Question 19

Difference between mass and weight?

Answer 19

Mass is a measure of how much matter there is in an object, while weight is a measure of the size of the pull of gravity on the object.

Question 20

How can friction be increased?

Answer 20

1) Making the surfaces rough. (there will be more irregularities. They will cause interlocking which in turn creates more frictional force)

2) By pressing the surfaces harder against each other (by increasing normal force). (more contact between the surface)

3) By increasing the surface area in contact.

4) using other sticky substances

Question 21

How can friction be decreased?

Answer 21

1) lubricating the surfaces. (oil/grease) (thin layer is formed there and moving surfaces do not directly rub against each other)

2) use of ball bearings (i.e. replacing sliding friction with rolling friction)

3) having a smoother surface (less irregularities which therefore produces less contact between the surface therefore reducing the frictional force)

4)streamlining the body.

Question 22

What is streamlining?

Answer 22

Designing the shape of an object specifically to reduce air/water resistance

Question 23

How can streamlining help with reducing air/water resistance?

Answer 23

Streamlining reduces air resistance because it reduces the surface area of the moving object that is put under a large force by the air.

Having a pointed-sharp shape is an idea of streamline as it helps reduce surface area of the moving object which is put under a large force by air therefore reducing friction.

Question 24

What are force pairs?

Answer 24

Two forces acting at the same point with equal magnitude but opposite direction.

resulting from Newton’s third law (“every action has an equal and opposite reaction”).

Question 25

What are balanced forces?

Answer 25

the total forces in opposite direction are equal in size.

If the forces are balanced, an object will either be stationary (not moving) or travelling at a constant or steady speed.

e.g.
A tug of war, where each team is pulling equally on the rope, is an example of balanced forces.
The forces exerted on the rope are equal in size and opposite in direction.
The rope will have an acceleration of zero under the action of these balanced forces.
It will therefore remain stationary.

Question 26

What are unbalanced forces?

Answer 26

the total forces in opposite directions are not equal in size.

If forces are unbalanced an object might start or stop moving, accelerate (get faster) or decelerate (get slower)

e.g.
The lift-off of a space rocket is an example of an unbalanced force in action. The space rocket accelerates upwards from its launch pad. The thrustfrom the rocket engines is greater than the weight of the rocket system. Because force thrust is greater than the force weight, the effect of one force does not cancel that of the other. The forces acting are unbalanced.

Question 27

stationary…

Answer 27

not moving / acceleration of 0

Question 28

what are resultant forces?

Answer 28

single force that could replace all the forces acting on an object (the resulting force is the result force in a force pair)

When two or more forces act on an object, the resultant force can be found by adding up the individual forces.

When forces are balanced, the resultant force is 0N as there is no difference in force and no acceleration/deceleration.

However, when forces are unbalanced, the resultant force is determined by the difference between the largest force and the smallest force in a direction in which it is travelling.

e.g.
If the weight of the box (acting downwards) is 50 N and the air resistance (acting upwards) is 20 N, the forces are unbalanced.

The resultant force is 30 N downwards.

Question 29

Formula for weight?

Answer 29

weight (N) = mass (kg) x gravitational field strength (N/kg)

Question 30

Formula for mass?

Answer 30

mass (kg) = weight(N) / gravitational field strength (N/kg)

Question 31

formula for gravitational field strength?

Answer 31

gravitational field strength (N/kg) = weight (N) / mass (kg)