P5- Forces Flashcards by William McCubbine

What are scalar quantities

Quantities which have magnitude only

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What are vector quantities

Quantities which have magnitude and direction

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What are examples of scalar quantities

Mass, temperature, speed, energy

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What are examples of vector quantities

Displacement, weight, force, velocity, acceleration

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What can be used to show the direction of the vector

An arrow head

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What type of quantity is a force

Vector quantity

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What is force measured in

Newtons

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What’s the two types of forces

Contact and noncontact

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What is a contact force

When two objects are physically touching

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What are examples of a contact force

Tension, Friction, air assistance and normal contact force

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What is a noncontact force

Two objects are physically separate

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What are examples of noncontact forces

Gravitational force, electrostatic force and magnetic force

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What quantity is mass and why

Mass is scaler as it has no direction

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Why is weight a vector quantity

Because the gravitational field strength causes a force downwards on the object

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What is gravitational field strength

A measure of the force of gravity in a particular location

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How do you calculate weight

Mass x Gravitational field strength

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What is the centre of mass

The single point where the weight acts on an object

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What’s a resultant force

A single force has the same effect as all the original forces acting together

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How is resultant force measured

Taking away the smaller force from the larger force

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How do you calculate work done

Force x distance

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What is elastic deformation

When elastic materials return to original size after force has acted on it

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What is inelastic deformation

When inelastic materials don’t return to original shape when the forces are removed

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What equation links force spring constant and extension

Force = spring constant x extension

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What is a moment

The turning effect of a force

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How do you calculate moment

Force x distance

What is a balance moment

When the clockwise moment equals anticlockwise moment

What is a lever

It allows large weight to be lifted with relatively small amount of force

What are fluids

Gas and liquids

What is the atmosphere

A thin layer of air around the Earth

What happens to the atmosphere when you increase the altitude

It gets less dense

What happens to atmospheric pressure with an increase in height

The pressure decreases

What is upthrust

The resultant force caused by the greater pressure on the bottom of the surface then on top of the surface

What is distance

How far an object has moved

What is displacement

The distance an object moves in a straight line and in what direction

What is a normal walking speed

1. 5 m/s

What is a normal running speed

3 m/s

What is a typical cycling speed

6 m/s

What factors does speed depend on

Age fitness terrain and distance

What is velocity

Speed and direction

Does the velocity change when an object moves at a constant speed in a circle

Yes because the direction changes

What does a distance time graph show

The distance travelled along a straight line

What is acceleration

The change in velocity over a period of time

What does the gradient of a velocity time graph show

Acceleration

When an object falls towards the surface of the Earth what is the acceleration of the object

9.8 m/s

What is terminal velocity

When an object stops accelerating and moves at a constant velocity

What is Newton’s first law of motion

If the resultant force acting on a stationary object is zero the object will remain stationary. Furthermore if the resultant force of a moving object is zero object to move at the same direction and speed.

What is newton second law of motion

The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object

What is inertia

The measure of how difficult it is to change the velocity of an object

What is Newton’s third law of motion

Whenever two objects interact, The forces they exert on each other are equal and opposite

1. What happens when a skydiver jumps out of the plane

The velocity increases as weight is the only force acting on the skydiver

Does the weight change during the skydive

No the weight Is always the same

2. What happens to the skydiver as it falls

The skydiver experiences friction with air molecules the force of friction acts upwards

2. As the skydiver falls, why does the diver continue to accelerate

The weight is greater than the air assistance

3. What is the effect of the velocity increasing

The air assistance increases

3. When does the skydiver reach terminal velocity

When the forces balance causing no resultant force and the velocity to be constant

4. When does the surface area of the skydive increase

When the parachute opens

4. What is the effect of the parachute opening and increasing the surface area

The air resistance increases meaning the result of forces acting upwards so the skydiver decelerates

5. When does the skydiver hit the ground

When the weight balances air resistance again but this time at a lower terminal velocity

What is the stopping distance

The total distance travelled from when the driver spots the obstruction to when the car stops

What is the thinking distance

The distance travelled by the car during the drivers reaction time

What is the reaction time

The time taken to spot the obstruction, make a decision and move the foot to the brake

What is the breaking distance

The distance the car travels from when the driver applies the brakes to when the car stops

What’s a typical reaction time

0.2 to 0.9 seconds

What factors increase reaction time

Alcohol drugs tiredness distractions

What factors increase breaking distance

Wet or icy conditions, Worn tires

What factors increase breaking distance

Wet or icy conditions, Worn tires

What happens during breaking in a car

Friction increases between the brake and the wheel, this causes kinetic energy to convert to thermal energy meaning the temperature increases at the brake

How much momentum does a stationary object have

Zero

What is the conservation of momentum

In a close system the total momentum before an event is equal to the total momentum after an event

Describe what happens during a car crash in terms of momentum

The momentum of the passengers decreases rapidly from large Amount to 0 in less than a second. This places huge forces on passengers

How can the danger of huge forces of momentum be decreased

By increasing the time of impact

What components within a car help to slow down momentum change

Airbags and seatbelts