[P5] Forces

What is meant by a vector quantity?

a quantity with magnitude and direction

What is meant by a scalar quantity?

a quantity with magnitude only

Give 5 examples of vector quantities (adfmv)

acceleration

displacement

force

momentum

velocity

Give 5 examples of scalar quantities (dmstt)

distance

mass

speed

temperature

time

What is a force?

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

Is force a scalar or vector quantity?

Vector

What are the two types of forces?

Contact and non-contact

What is a contact force?

Forces which act when the object causing the force and the object experiencing the force are touching

What ia a non-contact force?

Forces which act even when the object causing the force and the object experiencing the force are not touching

What is gravity?

The force of attraction between masses

How are weight and mass different? (3)

Mass is a measure of the amount of matter in an object, so remains the same everywhere

Weight is a force which acts on an object due to gravity

A measurement of weight could change with location

What can be used to measure mass?

A mass balance (balancing scales)

What can be used to measure weight?

A calibrated spring balance (newtonmeter)

Mass and weight are directly proportional. What formula links them?

Weight = mass x gravitational field strength

What is the unit for weight?

Newtons (N)

What is the unit for mass?

kg

What is the unit for gravitational field strength?

N/kg

What is a resultant force?

the overall force acting on an object

How is the resultant force acting on an object calculated?

by adding any forces acting in the same direction, and subtracting any forces acting in opposite directions

When is work done to an object?

when a force moves the object through a distance

What is 'work done'?

the energy transferred to an object by a force

What equation can be used to find work done?

Work done = force x distance

What unit is equivalent to 1 newton-metre?

1 Joule

What energy store increases when work is done against friction?

thermal store (the object's temperature increases)

What is elastic deformation?

Where an object returns to its original shape after the force deforming it is removed

What is inelastic deformation?

Where an object doesn't return to its original shape after the force deforming it is removed

What is meant by the limit of proportionality (in the context of springs)? (2)

The point where a spring's extension stops being proportional to the force applied to it

A plotted graph would become non-linear at this point

What equation is used to find the force applied to a spring when stretching/compressing it?

F = spring constant x extension

What is the moment of a force?

The turning effect of a force

What are the correct units for moment?

Newton meters, Nm

What are pivots?

The point about which an object will rotate

What measurement for distance should be taken when calculating moments?

The perpendicular distance from the pivot

What are levers?

Simple machines that increase the distance from the pivot to minimise the force required

What happens in terms of moments when an object is balanced (in equilibrium)?

The total clockwise moments are equal to the total anticlockwise moments

In gears, what happens when the driving gear is made smaller?

It will rotate quicker with a smaller moment

In gears, what happens when the driving gear is made larger?

It will rotate slower with a greater moment

How does increasing the radius of a gear affect the turning effect?

It increases proportionally

What state can a fluid be?

Liquid or gas

In what direction is the pressure from fluids exerted?

At right angles to the surface

How does increasing the coloumn height affect fluid pressure?

It increases proportionally

How does increasing the density affect fluid pressure?

It increases proportionally

What happens to the density of the atmosphere at greater altitudes?

It decreases

What produces atmospheric pressure?

Air molecules colliding with a surface

Why does atmosphere pressure decrease with an increase in height?

The number of air molecules above a surface decreases as the height of the surface above ground level increases

What is the difference between distance and displacement? (5)

Distance is how far an object moves

Distance does not involve direction

Distance is a scalar quantity

Displacement includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line

Displacement is a vector quantity

What is velocity?

Speed in a given direction

What is the difference between speed and velocity? (5)

Speed is how fast something moves

Speed does not involve direction

Speed is a scalar quantity

The velocity of an object is its speed in a given direction

Velocity is a vector quantity

What is an average human walking speed?

around 1.5 m/s

What is an average human running speed?

around 3 m/s

What is an average human cycling speed?

around 6 m/s

What is an average value for the speed of sound in air?

around 330 m/s

Describe the speed and velocity of an object travelling in a circle (2)

constant speed

changing velocity

How can you find the speed of an object from a distance-time graph?

calculating the gradient

What is acceleration?

how quickly an object changes its velocity

What equation is used to calculate acceleration?

acceleration = change in velocity / time

What does 'decelerating' mean?

an object is changing its speed by slowing down

How can you find the acceleration of an object from a velocity-time graph?

by calculating the gradient

How can you find the displacement of an object from a velocity-time graph?

by finding the area under the line of the graph

How do objects reach terminal velocity? (3)

An object falling through a fluid initially accelerates due to the force of gravity

Eventually, the upwards force due to air resistance will be equal to the downwards force due to gravity

The resultant force is zero and the object has reached terminal velocity

What is Newton's 1st law?

If the resultant force on an object is zero, its motion does not change

What is inertia?

The tendency for objects to continue in their state of rest or in uniform motion (like in Newton's first law)

What is Newton's 2nd law?

An object's acceleration is directly proportional to the resultant force acting on it, and inversely proportional to its mass

What does an object's inertial mass measure?

How difficult it is to change the object's velocity

How would you find an object's inertial mass? (2)

mass = force / acceleration

inertial mass is the ratio of force over acceleration

What does the symbol ~ mean?

approximately

What is Newton's 3rd law?

Whenever two objects interact, the forces they will exert equal and opposite forces on eachother

What is stopping distance?

the distance a vehicle travels during the driver thinking and the driver braking

What is a typical human reaction time?

0.2 - 0.9 seconds

What factors affect a driver's reaction time? (4)

Tiredness

drugs

alcohol

distractions

What factors affect braking distance? (4)

poor road conditions (wet or icy)

poor weather conditions

poor vehicle conditions (brakes or tyres)

reaction time

What happens to energy stores when a vehicle's brakes are applied? (2)

Work is done by the friction force between the brakes and the wheel

This reduces the kinetic energy of the vehicle and increases the thermal store (temperature) of the brakes

Why is applying the brake too hard/quickly dangerous?

Very large decelerations may cause brakes to overheat or loss of control of the vehicle

What is momentum? (2)

How difficult it is to stop an object in motion

It can be defined as "mass in motion"

What equation is used to find an object's momentum?

momentum = mass x velocity

What is the unit for momentum?

kg m/s

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 the event

What expression can be used to represent the change in momentum?

m Δv

How can the momentum of an object be changed?

By applying a force

What is the rate of change of momentum equivalent to?

The force applied

How do crumple zones affect collision times?

Through changing the shape of the car they increase collision times

How does increasing collision time affect the force of the collision?

Decreases force of the collision

What is terminal velocity?

The maximum speed reached when the resultant force on an object is 0N