Acceleration

Question 1

What is a force and what unit are they measured in?

Answer 1

A force is a push or pull upon an object in a particular direction. They result from the object’s interaction with another object. Force is measured in newtons, N.

Question 2

Give three examples of forces.

Answer 2

Contact:
Push, pull, buoyancy/upthrust, drag/air resistance, friction, reaction force, tension
Non contact:
Electrostatic, magnetic, gravitational (weight)

Question 3

List the possible effects of a resultant force acting on an object.

Answer 3

A resultant force is a single vector representing the net (overall) effect of all of the forces acting on an object
Acceleration (change speed or direction), Change shape.

Question 4

what is resultant force?

Answer 4

This is the size of the overall force acting on an object
When the forces are balanced the resultant force is zero.
When the forces are unbalanced the resultant force is equal to the size of the unbalanced force.

Question 5

What happens to an object if the forces are balanced?

Answer 5

It maintains a constant velocity (doesn’t accelerate).
If it isn’t moving it will stay stationary.
If it’s already moving it will continue to move in the same direction at a constant speed.

Question 6

What happens to an object if the forces are unbalanced?

Answer 6

It will accelerate:
Speed up
Slow down
Change direction.

Question 7

Newton’s first law:

Answer 7

Key point:
A resultant force will cause acceleration.
This will cause an object to:
change speed
and/or change direction

Question 8

what factors affect acceleration?

Answer 8

mass

Question 9

Newton’s Second Law

Answer 9

This states that the acceleration of an object is:
Directly proportional to the resultant force on the object.
a ∝ F
(Double the force = double the acceleration)
Inversely proportional to the mass of the object.
a ∝ 1/m
(Double the mass = half the acceleration)

Question 10

acceleration equation

Answer 10

acceleration = force /mass

Question 11

How does a resultant force affect velocity?

Answer 11

If resultant force is acting in the same direction as velocity then the object will accelerate and the velocity will increase.

If resultant force is acting in the opposite direction as velocity then the object will decelerate and the velocity will decrease.

Question 12

Inertia

Answer 12

The tendency of an object to continue on the course its on (i.e., move at a constant velocity) is called its inertia.

It will be more difficult to make an object with lots of inertia to accelerate than one with less inertia.

The inertial mass of an object is a measure of how difficult it is to change the object’s velocity.

Question 13

inertia equation:

Answer 13

Inertial mass = force / acceleration

Question 14

what is mass

Answer 14

The mass of an object is related to the amount of matter it contains.
Mass is not changed by gravitational forces.
Mass is measured in kilograms (kg) using a balance

Question 15

what is weight

Answer 15

The weight of an object is the force due to gravity acting on it.
If the gravitational field changes, the weight changes. (The moon has a lower gravitational field strength so you would have less weight there!)
Scientists measure weight in newtons (N) using a newtonmeter.

Question 16

what is weight equal to?

Answer 16

weight = mass x gravitational field strength (9.8)

Question 17

what is falling due to

Answer 17

Falling is due to weight - the force caused by gravity acting on the mass of an object.
In the vacuum both objects only had weight acting on them.

Question 18

Drag

Answer 18

If an object is moving through a fluid (liquid or gas) there is a drag force acting on it.
This force is caused because the object has to push the fluid particles out of the way
The fluid particles therefore push on the object in the opposite direction with the same amount of force (Newton’s third law).

Question 19

3 things increase the size of the drag force:

Answer 19

Speed of object
Shape of object - wide flat shapes cause more drag
Viscosity of the liquid (how ‘thick’ it is)
Speed - The drag force increases as the speed increases, because the faster the object moves the more particles it hits every second.

Question 20

The acceleration of the object decreases as it falls because

Answer 20

The drag force increases as the object speeds up.
So the resultant force on the object decreases so the rate of also acceleration decreases.

Question 21

When drag force = weight…..

Answer 21

the resultant force is equal to zero. The object stops accelerating, it has reached terminal velocity.

Question 22

The stopping distance of a car can be split into 2 parts:

Answer 22

Thinking distance
Braking distance

Question 23

what is thinking distance

Answer 23

The thinking distance is the distance travelled during the reaction time of the driver.

Question 24

what is braking distance

Answer 24

The braking distance is the distance travelled while the brakes are applied.

Question 25

What factors affect reaction time?

Answer 25

Tiredness
Drugs / alcohol
Age
Distractions (eg mobile phone)

Question 26

factors that affect thinking distance:

Answer 26

Initial velocity
Reaction time

Question 27

what is thinking distance equal to?

Answer 27

Thinking distance = initial velocity x reaction time

Question 28

factors that affect braking distance?

Answer 28

Initial velocity
Mass of vehicle
Size of braking force applied
Condition of vehicle (esp tyres, brake pads and discs)
Road surface (eg water, ice, gravel)

Question 29

If the braking force applied is too big it can lead to:

Answer 29

Skidding and loss of control
The brakes overheating - they could even catch fire

Question 30

This energy is transferred by friction to maximise we need:

Answer 30

Good brake pads and discs
Good road conditions
Tyres with good grip

Question 31

Calculating Acceleration

Answer 31

a = v2 – u2/ 2s

Question 32

In a closed system momentum is always ………..

Answer 32

In a closed system momentum is always conserved
This means the total momentum in a system before an event is equal to the total momentum after the event.

Question 33

momentum equation

Answer 33

Momentum (p) = mass (m) x velocity (v

Question 34

Closed system

Answer 34

Closed system - a group of objects whose total mass remains constant and that are not subject to any external forces.

If an external force acts on a system energy will be transfers to or from it and momentum will not be conserved.