Physics forces year 9

what is the difference between scalar and vector quantities?

scalar quantities- have magnitude(size) only

vector quantities- have magnitude and direction shown by an arrow( the length represents the magnitude and direction of arrow represents direction)

Give examples of both scalar and vector quantities:

scalar: mass, temperature, speed, energy, time, distance

vector: displacement, weight, force, velocity, acceleration, momentum

what is a force?

a force is a push or a pull that acts on an object due to the interaction with another object(N)

state and describe the 2 types of forces:

contact and non-contact forces,

contact forces - the objects are physically touching

non-contact- the objects are physically separated.

Give examples for non-contact and contact forces:

contact: friction, air-resistance, tension, and normal contact force

non-contact- gravitational force, electrostatic force, and magnetic force

what is gravity, mass, and weight? state the equation linking them together:

gravity- force of attraction between all objects

mass- measure of the amount of matter in an object

weight- force acting on an object due to gravity

weight = mass x gravitational field strength( the force of gravity acting on a mass of one kilogram at a specific location)

what is the weight depend on and directly proportionate to?

weight depends on gravitational field strength at the point where the object is

weight is directly proportionate to the mass

what is the ‘centre of mass’? what is used to measure weight?

The weight of an object may be considered to act at a single point referred to as the object’s ‘centre of mass’

weight is measured using a newtonmeter

what is a resultant force?

the single force that has the same effect as all the forces acting on an object

what is the difference between distance and displacement?

distance is how far an object moves, it doesn’t involve direction, so it is a scalar quantity.

displacement includes both the distance distance (measured in a straight line from point to point) and direction of that line, so it is a vector quantity.

what is speed?

the distance the object travelled in a given time, it does not involve direction so it a scalar quantity?

what is the formula triangle for speed, distance and time?

distance/ s is at the top

what are the average speeds for 1) walking 2) running and 3) cycling

1) 1.5m/s 2) 3m/s 3) 6m/s

Is speed constant and what are the factors that can affect speed?

speed of a moving object is rarely constant, it is constantly changing because of factors such as age, terrain, fitness and distance travelled. e.g. people who run long distance run faster at the start when they are less tired

what are speeds for 1) a car on the main road 2) a fast train in UK 3) a cruising aeroplane 4) sound

1) 13m/s 2) 50m/s 3) 250m/s 4) 330m/s

what speed can also vary other than moving objects?

the speed of sound and air

what is velocity and why is it a vector quantity?

the velocity is the speed but including the direction, for example 20m/s east, that is why it is a vector quantity

What is the special case for velocity and explain why?

if an object moves at a constant speed in a circle then its velocity is constantly changing even though its speed is constant, for example a race car moving around a circular race track at a constant speed direction is constantly changing, therefore its velocity changes as well.

what is acceleration and the equation to calculate it?

The acceleration tells us the change in velocity over a given time.

acceleration = change in velocity/ time

On a velocity time graph how do you find the acceleration and what does a horizontal line represent?

By calculating the gradient

a horizontal line represents that the object is moving at a constant speed

How do you calculate the displacement in a velocity time graph

the total area under the graph

What is the acceleration of objects falling freely under gravity near the Earth’s surface?

9.8 m/s2

Describe the acceleration of a object falling through fluid?

initially accelerates due to force of gravity. Eventually, resultant force will be zero and the object will move at its terminal velocity

What is Newtons first law of motion?

According to Newton's first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:

• a stationary object stays stationary

• a moving object continues to move at the same velocity (at the same speed and in the same direction)

What is newtons third law of motion and when does it apply?

whenever two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.

It applies when objects are in an equilibrium position( a state of balance, where opposing forces or influences are equal, resulting in stability)

what is the stopping distance?

The total distance travelled from when the driver first spots the obstruction to when the car stops, and it can split into 2 parts: the braking distance and the stopping distance.

what is the thinking distance and factors which affect it?

the distance travelled by the car during the the drivers reaction time( time taken for driver to spot obstruction, make a decision and then move their foot to the brake)

Factors: tiredness, drugs, alcohol, distractions

what is the braking distance and factors which affect it?

the distance the car travels from when the driver applies the brake to when the car stops

Factors: wet and icy conditions, brakes and tires condition