P4- Explaining Motion

Question 1

Distance time graph?

Answer 1

• Gradient= speed
• Flat sections= stationary
• Steeper slope= faster it’s going
• “downhill” sections means it’s coming back to starting point
• Curves- acceleration and deceleration
• Steeper curves- faster
• Levelling off curves- decelerating

Question 2

Displacement graphs?

Answer 2

• The gradient tells you the velocity.
• Can be positive or negative
• Everything else is the same as distance time graphs.

Question 3

What is velocity?

Answer 3

• Describes speed and direction.
• Instantaneous velocity is the speed and direction at a given moment in time.
• You can have negative velocities.

Question 4

What is acceleration?

Answer 4

Acceleration is the change in velocity (or speed) in a certain amount of time.

Question 5

Acceleration formula?

Answer 5

Acceleration (m/s squared) = change in velocity (m/s) / time taken (s)

Question 6

Velocity time graphs?

Answer 6

• Gradient = acceleration
• Flat sections = constant speed
• Steeper gradient = greater acceleration/deceleration
• Uphill section (/) are acceleration
• Downhill sections () are deceleration
• A curve means changing acceleration
• Negative velocity means the object is travelling in the opposite direction.

Question 7

What is gravitational potential energy?

Answer 7

It is energy stored in an object when you raise it to a height against the force of gravity.

Question 8

Equation for GPE?

Answer 8

Change in gravitational potential energy (J) = Weight (N) * Vertical height difference (m)

Question 9

Conversion of GPE to KE?

Answer 9

When something falls its gravitational potential energy (GPE) converts to kinetic energy (KE).

Question 10

Equation for GPE to KE?

Answer 10

KE gained = GPE lost

Question 11

What is kinetic energy?

Answer 11

Anything that’s moving has kinetic energy. The kinetic energy of something depends on its mass and speed.

Question 12

Equation for kinetic energy?

Answer 12

Kinetic energy (J) = mass (kg) * velocity squared. (m/s squared)

Question 13

How do you increases something’s KE?

Answer 13

To increase something’s kinetic energy you need to increase its velocity.

To increase the velocity you apply force to it.

Question 14

What does it mean when energy is conserved?

Answer 14

This means you can’t create or destroy energy. It gets transformed into one kind of energy to another.

Question 15

Why is energy lost while work is done?

Answer 15

The increase in an object KE is normally a bit less than the amount of work done on it, because some energy is wasted as heat.

Question 16

What does “work done” mean?

Answer 16

When a force moves on an object it does work and energy is transferred to the object.

Question 17

Work done equation?

Answer 17

Amount of energy transferred (j) = work done (j)

Question 18

Work done by a force equation?

Answer 18

Work done by a force (J) = force (N) * distance moved in direction of force (m)

Question 19

Change of momentum equation?

Answer 19

Change of momentum (kg m/s) = resultant force (N) * Time for which the force acts (s)

Question 20

Car safety features?

Answer 20

• Crumple zones- crumple on impact- increases the time taken for the car to stop.
• Air bags- Slows you down gradually.
• Seat belts- increases the time taken for the wearer to stop. This reduces the forces acting on the chest.
• Cycle and motorcycle helmets- provides padding that increases the time taken for your head to come to a stop if it hits something hard.

Question 21

Arrows representing forces?

Answer 21

• The length of the arrow shows the size of the force.
• The direction of the arrow shows the direction of the force.
• When arrows are opposite but are all the same size. The forces are balanced.

Question 22

What is the resultant force?

Answer 22

It is the overall force acting on the object. You can get this amount by adding the individual forces.

Question 23

What are an interaction pair of forces?

Answer 23

When an object exerts a force it always experiences a force in return. This is called interaction pair of forces.

Question 24

What is a reaction force?

Answer 24

It is a force which is a “response” to an object which exerts a force on it.

For example, if you put a book on a table, the book pushes on the table with a force equal to its weight.

And the table exerts an equal and opposite force upwards on the book. That is called the reaction force.

Question 25

What is friction?

Answer 25

When an object is moving relative to another one, both objects experience a force in the direction that opposes the movement - this is friction.

Question 26

Is friction a reaction force?

Answer 26

• Friction is a reaction force- it happens as a result of an applied force.

Question 27

Friction between solid surfaces which are gripping?

Answer 27

This type of friction is gripping.

It lets you walk the friction between your shoes and the ground allows you to push against it and move forwards.

Question 28

Friction between solid surfaces which are slipping??

Answer 28

Two objects slide past each other.

You can reduce sliding friction and gripping friction by adding a lubricant like grease or oil between the surfaces.

Question 29

What is drag?

Answer 29

Drag is a type of friction.

An object moving through a fluid has to force its way past the molecules in the fluid. This causes friction.

Drag only happens to objects moving through the water.

Question 30

Acceleration?

Answer 30

If a car exerts a bigger driving force (forwards) than the drag counter forces (backwards) the car will accelerate.

Question 31

Deceleration?

Answer 31

If the driving force is less than the drag - the car will slow down.

Question 32

Momentum??

Answer 32

This means how hard it is to stop it.

The greater the mass of an object the greater the momentum.

Question 33

Momentum equation??

Answer 33

Momentum (kg m/s) = mass (kg) * velocity (m/s)

Question 34

Equation for speed?

Answer 34

Speed (m/s) = distance travelled (m) / time taken (s)