Motion And Forces

Question 1

What is the resultant force?

Answer 1

The total force from two or more forces acting upon a single object.

Question 2

How do you work out the resultant force?

Answer 2

If the forces are acting in the same direction add them

It they are acting in opposite directions subtract one from the other

Question 3

If the resultant forces on an object is zero, what do we say the forces are?

Answer 3

Balanced

Question 4

If there is a non-zero resultant force on an object, what are the forces?

Answer 4

Unbalanced

Question 5

What is mass?

Answer 5

The quantity of matter their is in an object, and only changes if the object itself changes

Question 6

What is weight?

Answer 6

Weight is a measure of the pull of gravity on an object and depends on the strength of gravity

Question 7

How can weight be measured?

Answer 7

Using a force meter, which has a scale in newtons

Question 8

On Earth what is the gravitational field strength?

Answer 8

It has a value of about 10 newtons per kilo gram (N/kg). This means that each kilogram is pulled down with a force of 10N. The gravitational field strength is different on other planets and moons

Question 9

What is the equation for weight?

Answer 9

Weight = mass ✖️ gravitational field strength

Question 10

On Earth a falling object has a force other than weight, what is it?

Answer 10

Air resistance

Question 11

What is the acceleration of an object?

Answer 11

A measure of how much it’s velocity changes in a certain time

Question 12

What is Newton’s second law?

Answer 12

The acceleration in the direction of a resultant force depends in:
The size of the force (for the same mass, the bigger the force the bigger the acceleration)
The mass of an object (force the same force, the more massive the object the smaller the acceleration)

Question 13

What is the equation for force?

Answer 13

Force = mass ✖️ acceleration

Question 14

Explain inertial mass

Answer 14

The more massive an object is, the more force is needed to change its velocity (either to make it start moving or to change the velocity of a moving object)

Question 15

Define inertial mass

Answer 15

We define the inertial mass of an object as the force on it divided by the acceleration that the force produces

Question 16

What is the size of a force represented by?

Answer 16

The size of the arrows

Question 17

what can Newton’s first law be written as?

Answer 17

A moving object will continue to move at the same speed and direction unless an external force acts on it
A stationary object will remain at rest unless an external force acts on it

Question 18

Explain centripetal force

Answer 18

An object moving in a circle has changing velocity, even though it’s speed remains the same. The resultant force that causes the change in direction is called the centripetal force and acts towards the centre of the circle

Question 19

Newton’s third law is about the forces on two different objects when they interact with each other. What interaction can happen?

Answer 19

When objects touch, such as when you sit on a chair

At a distance, such as the gravitational attraction between the earth and the moon

Question 20

What are action-reaction pairs?

Answer 20

A pair of forces acting on two interactive objects. The two forces are always the same size and in opposite directions

Question 21

What is equilibrium?

Answer 21

When a situation is not changing because all the things affecting it balances out

Question 22

Action-reaction forces are not the same as balanced forces. In both cases the sizes of the forces are equal and act in opposite directions, but what?

Answer 22

Action-reaction forces act on different objects

Balanced forces all act in the same object

Question 23

Explain collisions in action-reaction pairs?

Answer 23

The action and reaction forces that occur during the collision are the same size but they do not necessarily have the same effects on the two objects, because the objects have different masses

Question 24

What is momentum?

Answer 24

Momentum is a measure of the tendency of an object to keep moving - or of how hard it is to stop it moving. The momentum of an object depends on its mass and velocity. Momentum spends on a vector quantity (velocity) and is also a vector

Question 25

How is momentum calculated?

Answer 25

Momentum = mass ✖️ velocity

Question 26

What is conservation of momentum?

Answer 26

When moving objects collide the total momentum of both objects is the same before the collision as it is after the collision as long as there are no external forces acting

Question 27

For momentum, if two objects are moving in opposite directions what do we do?

Answer 27

We give the momentum of one object a positive sign and the other the negative sign

Question 28

What is thinking distance?

Answer 28

The distance travelled by a vehicle which the driver reacts

Question 29

What is breaking distance?

Answer 29

The distance travelled by a vehicle while the brakes are working to bring it to a halt

Question 30

What is stopping distance?

Answer 30

The distance in which a car stops, which is the sum of the thinking and breaking distances

Question 31

How do you work out stopping distance..

Answer 31

Thinking distance + breaking distance

Question 32

What is reaction time?

Answer 32

A reaction time is the time between a person detecting a stimulus (such as a flashing light or a sound) and their response (such as pressing a button or applying breakers in a car)

Question 33

How can response times be measured?

Answer 33

Using a computer or electric circuits that measure the time between a stimulus and a response

Question 34

What is the typical reaction time to a visual stimulus such as a computer screen changing colour?

Answer 34

About 0.25 seconds

Question 35

Why would a reaction time increase?

Answer 35

If the person is:
Tired
ill
Been taking drugs 
Drinking alcohol
Distracted

Question 36

If a vehicle has more mass, more force is needed to decelerate it, so if the same amount of friction is used to stop a vehicle, what will happen?

Answer 36

A heavier vehicle will travel further than a lighter one, it has a greater braking distance

Question 37

The force used to accelerate an object transfers energy to it. What does the amount of energy depend on?

Answer 37

It depends on the size of the force and how far the object moves while the force is pushing it . The energy transferred by a force acting over a distance is called work done?

Question 38

What is work done?

Answer 38

A measure of the energy transferred when a force acts through a distance

Question 39

How do you calculate work done?

Answer 39

Work done = force ✖️ distance moved in the direction of the force

Question 40

What is kinetic energy?

Answer 40

The energy stored in a moving object

The amount of kinetic energy depends on the mass of an object and its velocity

Question 41

How do you work out Kinetic energy?

Answer 41

Kinetic energy = 1/2 ✖️ mass ✖️ (speed) squared

Question 42

The breaking distance of a car depends on its kinetic energy, and so depends on the square of its velocity. What does this mean?

Answer 42

This means that is the velocity doubles, the braking distance is multiplied by 2 squares which is 4

Question 43

When a vehicle stops the kinetic energy is transferred to other energy stores by the breaking force. What can we use this idea to calculate?

Answer 43

The braking distance if a vehicle

Question 44

What is slowing down?

Answer 44

Deceleration

Question 45

What does the force for any kind of acceleration depend on?

Answer 45

The size of the acceleration and the mass of an object

Question 46

What are built into the front (and sometimes the back) of cars?

Answer 46

Crumple zones, which is a safety feature, if the car hits something it takes a little time for this crumpling to happen, so the deceleration of the car is less and the force of the car is also less than if it had a more solid front

Question 47

What do airbags increase the time of?

Answer 47

Increases the time it takes for a persons head to stop in a collision

Question 48

What does the force in the road depend on?

Answer 48

The change in momentum as the car comes a stop