Forces, speed, Newton's laws of motion, braking and momentum

What is the difference between distance and displacement?

Distance is a scalar quantity with magnitude only; displacement is a vector quantity with both magnitude and direction.

What is the difference between speed and velocity?

Speed is a scalar quantity with magnitude only; velocity is a vector quantity with both magnitude and direction.

What factors can affect the speed at which someone walks, runs, or cycles?

Age, fitness, terrain, and distance travelled.

What are typical speeds for a person walking, running, and cycling?

1.5 m/s, 3.0 m/s, and 6.0 m/s respectively.

What are typical speeds of a car and a train?

13-30 m/s and 50 m/s respectively.

What is a typical speed for sound travelling in air?

330 m/s.

What is acceleration?

Change in velocity of an object per second.

What is the unit of acceleration?

m/s².

How can an object be accelerating even if it is travelling at a steady speed?

If it is changing direction.

What is happening to an object if it has a negative acceleration?

It is slowing down.

What information does the gradient of the line in a distance-time graph provide?

Speed.

What information does the gradient of the line in a velocity-time graph provide?

Acceleration.

How can the distance travelled by an object be found from its velocity-time graph?

Calculate the area under the graph.

What is the acceleration of a free-falling object due to gravity?

~9.8 m/s².

What is the name for the steady speed a falling object reaches when the resistive force is equal to its weight?

Terminal velocity.

What is the general name for the frictional forces an object experiences when moving through a fluid?

Drag.

In which direction does the drag on an object always act?

In the direction opposite to which it is moving.

What happens to the drag on an object as its speed increases?

The drag increases.

What can be done to reduce the drag on an object?

Streamlining.

What is the name given to the distance a vehicle travels to safely come to a stop after the driver has spotted a hazard?

Stopping distance.

What is thinking distance?

The distance a vehicle travels during the driver's reaction time.

What is braking distance?

The distance a vehicle travels once brakes have been applied.

What is the relationship between stopping distance, thinking distance, and braking distance?

Stopping distance = thinking distance + braking distance.

Does the speed of a vehicle have a bigger effect on braking distance or thinking distance?

Braking distance.

Which distance is proportional to the speed of the vehicle?

Thinking distance.

Which distance increases by an increasing amount as speed increases?

Braking distance.

What are three factors that can affect the braking distance of a vehicle?

Speed, road conditions, condition of tyres and brakes.

What is the definition of one joule of work?

The work done when 1 N of force causes 1 m displacement.

What happens if the braking force used to stop a vehicle is very large?

Brakes may overheat or the car may skid.

What is the law of conservation of momentum?

In a closed system, the total momentum before an event is equal to the total momentum after it.

How is the force acting on an object related to its momentum?

Force acting on an object = rate of change of momentum.

What are examples of everyday safety features which work by increasing the time taken for the change in momentum?

Air bags, seat belts, crumple zones in cars, cycle helmets, crash mats in gyms, cushioned surfaces in children's playgrounds.

What do we mean by inertia?

The tendency of an object to remain in a steady state (at rest or in uniform motion).

What does Newton's First Law say?

An object will remain at rest or in uniform motion unless acted upon by a resultant force.

What is the resultant force on a stationary object?

Zero.

What is the resultant force on an object moving at a steady speed in a straight line?

Zero.

What will an object experience if the resultant force on it is not zero?

It will accelerate.

What is the name of the tendency of an object to remain in a steady state at rest or moving in a straight line at a constant speed?

Inertia.

What forces are balanced when an object travels at a steady speed?

Resistive forces = driving force.

According to Newton's Second Law, what is the acceleration of an object proportional to?

The resultant force acting on it.

According to Newton's Second Law, what is the acceleration of an object inversely proportional to?

The mass of the object.

What is the inertial mass of an object?

How difficult it is to change an object's velocity.

What does Newton's Third Law say?

When two objects interact, they exert equal and opposite forces on each other.

Starting to move, stopping moving, speeding up, slowing down, and changing directions are all examples of which physical process?

Acceleration/change in velocity

What is a scalar quantity?

A quantity that only has size (magnitude).

What is a vector quantity?

A quantity that has both size and direction.

What is a force?

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

Is force a vector or scalar quantity?

Vector.

What is a contact force?

A force when objects are physically touching.

What is a non-contact force?

A force when objects are physically separated.

What is the size of the resultant force on an object if the forces on it are balanced?

Zero.

What is the name for the force acting on an object due to gravity?

Weight.

What instrument can be used to measure the weight of an object?

Calibrated spring-balance (newtonmeter).

What is the centre of mass?

The point through which the weight of an object can be considered to act.

What is elastic deformation?

An object can go back to its original shape and size when deforming forces are removed.

What is inelastic deformation?

An object does not go back to its original shape and size when deforming forces are removed.

How do you find the spring constant from a force-extension graph of a spring?

Find the gradient of the straight line section.

What is the turning effect of a force called?

Moment.

What can you say about clockwise and anticlockwise moments on a balanced object?

They are equal.

How does a lever reduce the amount of force needed to create a particular sized moment?

By increasing the distance from the pivot.

What happens to the moment of a force when a small gear drives a large gear?

The moment is increased.

Why does the temperature of a vehicle’s brakes increase when the brakes are applied?

work done by the frictional force between the brakes and wheels transfers energy from the kinetic energy store of the car to the thermal energy store of the brakes

What does m/_\v stand for?

change in momentum

What is the same about the interaction pair of forces when two objects interact with eachother?

the forces are the same size

What is different about the interaction pair of forces when two objects interact with each other?

forces are in opposite directions