Force (2) - Motion

How can an object accelerate without changing speed?

Changing direction

What type of quantity is distance?

Scalar

What type of quantity is displacement?

Vector

State the equation linking distance travelled, speed and time using symbols.

s = vt

What does the word 'final' mean?

At the end

State the equation linking mass, velocity and momentum in words.

Momentum = Mass x Velocity

What does the word decelerating mean?

Slowing down

State the unit of acceleration.

Metres per second squared or m/s²

State the equation linking acceleration, change in velocity and time taken in words.

Change in velocity = Acceleration x Time taken

State a typical value of speed for a car or ship.

13 m/s

What symbol is used instead of writing the words 'distance travelled'?

s

State a typical value of speed for a train.

27 m/s

What does a horizontal line on a distance-time graph show?

No motion/stationary

State the range of typical reaction time values.

0\.2 - 0.9 seconds

How does speed affect stopping distance?

Greater speed, greater stopping distance

State the unit of time.

Seconds OR s

How do you calculate average speed?

Total distance divided by total time

Complete this sentence: The less steep the line on a distance-time graph is…

… the slower the speed

What 3 changes are considered 'acceleration' in physics?

Speeding up, slowing down and changing direction

What type of quantity is velocity?

Vector

What is terminal velocity?

The maximum speed an object can reach

How can thinking distance be calculated?

Thinking distance = speed x reaction time

What does a straight line (not horizontal) on a distance-time graph show?

Constant speed

What is the acceleration of an object falling freely under gravity near the Earth's surface?

9\.8 m/s²

When an object's velocity and acceleration are in the same direction, what happens to the object's motion?

Speeds up

What does a resultant force cause?

Acceleration

State the unit of distance.

Metres OR m

Describe the energy transfers when force is applied to the brakes of a vehicle.

Kinetic energy of vehicle decreases. Thermal energy of the brakes increases.

State the unit of velocity.

Metres per second OR m/s

What phrase is used for 'the distance a vehicle travels under the braking force'?

Braking distance

Which quantity is the rate of change of distance or how much distance travelled per unit time?

Speed

What does the word 'initial' mean?

At the start

What does a curved line becoming steeper on a distance-time graph show?

Speeding up

What type of quantity is speed?

Scalar

What causes acceleration?

Resultant force

State 3 factors (apart from speed) which can increase braking distance.

Wet/icy conditions, poor condition of brakes or tyres, heavier mass

Which of Newton's laws explains why momentum is conserved?

Newton's 3rd law

When is momentum not conserved?

When there are external forces acting

How is the speed of an object calculated from a distance-time graph?

Gradient

State the equation linking mass, velocity and momentum using symbols.

p = mv

What symbol is used instead of writing the word 'time'?

t

What does the gradient of a velocity-time graph equal?

Acceleration

State the relationship between acceleration and resultant force when mass is constant.

Directly proportional

Define 'stopping distance'.

Thinking distance + Braking distance

Why does speed increase thinking distance?

Faster vehicle means greater distance travelled in the reaction time.

Which physics quantity means how far an object is from its starting point, including direction?

Displacement

How is the distance travelled by an object calculated from a velocity-time graph?

Area under graph

What is the resultant force at terminal velocity?

Zero

Why does a falling object accelerate initially?

Weight is bigger than air resistance

What does the gradient of a distance-time graph equal?

Speed

State a typical value of speed for a person walking.

1\.5 m/s

What is a system?

A group of objects that interact

State the equation used for Newton's 2nd law in words.

Resultant force = mass x acceleration

What symbol is used instead of writing the word 'acceleration'?

a

What is a closed system?

A system on which no external forces are acting

Define acceleration.

Rate of change of velocity

State a typical value of speed for a person cycling.

6 m/s

How do you calculate the speed from a distance-time graph if the line isn't straight?

Draw a tangent and find the gradient of the tangent

Why do wet/icy conditions and poor brake/tyre condition increase braking distance?

They decrease friction

An object continues at a constant velocity unless a resultant force acts on it. Which law?

Newton's 1st law

Name 2 types of 'event' covered by the conservation of momentum.

Collisions and explosions

What phrase is used for the time between seeing a hazard in the road and responding to it?

Reaction time

What phrase is used for 'the distance a vehicle travels during the driver's reaction time'?

Thinking distance

What symbol is used instead of writing the word 'speed'?

v

The tendency of objects to continue in their state of rest or of uniform motion is called… ?

Inertia

What does a curved line becoming less steep on a distance-time graph show?

Slowing down

Define the 'conservation of momentum'.

In a closed system, the total momentum before an event = the total momentum after the event

Complete this sentence: The steeper the line on a distance-time graph…

… the faster the speed

How is the acceleration of an object calculated from a velocity-time graph?

Gradient

Eventually a falling object will reach terminal velocity. Why?

Air resistance = weight, zero resultant force so no acceleration

Which quantity is the rate of change of displacement?

Velocity

When an object's velocity and acceleration are in opposite directions, what happens to the object's motion?

Slows down

State the relationship between acceleration and mass when resultant force is constant.

Inversely proportional

Acceleration is directly proportional to resultant force and inversely proportional to mass. Which law?

Newton's 2nd law

State the unit of displacement.

Metres OR m

Complete this law: Whenever two objects interact, the forces they exert on each other are…

Equal and opposite

What does a horizontal line on a velocity-time graph show?

Constant speed

If speed is changing, what word is used for the speed at a specific moment in time?

Instantaneous speed

If an object is stationary and there is a resultant force of 0 N acting on it, what does the object do?

Remains stationary

State the unit of momentum.

kilogram metres per second OR kgm/s

When an object is moving at a constant speed in a circle, it is accelerating. Why?

The object is changing direction, velocity is a vector quantity so velocity is changing

What symbol is used instead of writing the word 'momentum'?

p

It is safer to fall on soft surfaces because they reduce deceleration. Why is this safer?

Smaller deceleration means smaller force means less chance of injury

Complete this sentence: The steeper the line on a velocity-time graph…

… the greater the acceleration

What does a horizontal line along the x-axis on a velocity-time graph show?

No motion/stationary

As an object falls its acceleration decreases. Why?

Air resistance increases as speed increases so resultant force decreases

Complete this sentence: The less steep the line on a velocity-time graph is…

… the smaller the acceleration

Which physics quantity means how far an object moves, regardless of direction?

Distance

How do you calculate the acceleration from a velocity-time graph if the line isn't straight?

Draw a tangent and find the gradient of the tangent

State a typical value of speed for sound in air.

330 m/s

What type of quantity is momentum?

Vector

If the resultant force on an object acts in the same direction as its motion, what does the object do?

Speeds up

What word is used for a speed that doesn't change?

Constant speed OR Uniform speed

Why can large decelerations be dangerous?

Brakes overheating, loss of control/skid

State a typical value of speed for a plane.

250 m/s

Why does opening a parachute cause a sky diver to slow down?

Air resistance is bigger than weight

Why do tiredness, drugs, alcohol and distractions increase thinking distance?

They increase reaction time

State the unit of speed.

Metres per second OR m/s

How does speed affect air resistance?

As speed increases, air resistance increases

When an object is moving at a constant speed in a circle, its velocity is changing. Why?

The object is changing direction and velocity is a vector quantity.