Physics 2024

accelertion

The rate at which velocity changes

drag

resistance by friction from air or water moving over a surface

Gravity

A force of attraction between objects that is due to their masses.

reaction

a response to something

terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

air resistance

force that opposes the motion of objects that move through the air

elastic collision

A collision in which colliding objects rebound without lasting deformation or the generation of heat.

inertia

The tendency of an object to resist a change in motion

reference point

A place or object used for comparison to determine if an object is in motion

thrust

push with force

at rest

The state of an object when it is not in motion

extension

stretching or elongation

initial velocity

the starting velocity

scalar

A physical quantity that has magnitude only.

unbalanced forces

forces acting on an object that combine and form a net force that is not zero

average speed

total distance divided by total time

final velocity

velocity of an object at the end of a time interval

kinetic

energy of motion

speed

The distance an object travels per unit of time

upthrust

A force that pushes things up in liquids and gases.

balanced forces

Equal forces acting on an object in opposite directions

force

A push or pull exerted on an object

net force

The combination of all forces acting on an object

vector

A quantity that has magnitude and direction

deceleration

negative acceleration

free fall

the motion of a falling object when the only force acting on it is gravity

newton

SI unit of force

stationary

standing still; not moving

velocity

Speed in a given direction

Displacement

Distance and direction of an object's change in position from the starting point.

friction

A force that opposes motion between two surfaces that are in contact

normal force

the force perpendicular to a surface that prevents an object from falling through the surface

stretch

make long, longer or bigger

weight

A measure of the force of gravity on an object

force

an interaction between 2 systems and as a consequence it can change a system’s motion

contact forces

forces that have an effect only on objects that they touch

non-contact forces

the objects don't physically come into contact, e.g. gravity, magnetic force

Distance

is the actual path taken between two points A to B

Distance is a ____quantity - it only has ____ and not a direction

scalar
magnitude

Displacement

is the straight line journey from one point to another

The displacement B to A is the exact reverse of A to B (same magnitude but opposite direction)

The displacement is a _____ - it has a ____ and ______

vector, magnitude, direction

All vectors can be represented by ....

arrows showing the size and direction

scalar quantity

a quantity that can be described by magnitude only and has no direction

Examples of scalar quantities

vector quantities

examples of contact forces

friction, reaction force, upthrust, tension, air resistance

Friction

A force that opposes motion between two surfaces that are in contact

Two objects sliding past each other experience friction forces. For example, a box sliding down a slope.

reaction force

force acting in the opposite direction

An object at rest on a surface experiences reaction force. For example, a book on a table.

Upthrust

A force that pushes things up in liquids and gases.

An object that is partly, or completely, submerged in fluid experiences a greater pressure on its bottom surface than on its top surface. This causes a resultant force upwards. This force is called upthrust.

tension

stress that occurs when forces act to stretch an object

An object that is being stretched experiences a tension force. For example, a cable holding a ceiling lamp.

air resistance

force that opposes the motion of objects that move through the air

An object moving through the air experiences air resistance. For example, a skydiver falling through the air.

non-contact forces are ...

Gravitational force, magnetic force, electrostatic force

Gravitational force

an attractive force that acts between any two masses

electrostatic force

attraction or repulsion of particles or objects because of their electric charge.

magnetic force

the attraction or repulsion between magnetic poles

Are forces vector or scalar quantities? And what are they measured in?

Forces are vectors because they have both a size and a direction

Forces are represented using arrows

Forces are measured in newtons (N)

free body diagram

a diagram showing all the forces acting on an object

What forces are acting on a stationary student sat on a stool?

There are two forces to consider

the force of gravity downwards (the weight) and the normal contact force of the chair pushing you upwards

To simplify further, we only draw the forces and do not draw the body at all

This is called a free body diagram

balanced forces

When forces add up to zero (the resultant force is zero) then we say that they are balanced

If forces are balanced then the object will not change its motion

If the object was stationary then it will remain stationary

If the object was moving then it will remain moving at a constant speed

Newton's First Law

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

The car is either stationary or moving in a straight line at a constant speed.

unbalanced forces

If forces are unbalanced then the resultant force will be non-zero

The consequence will be that an object will change its motion

The object will accelerate or decelerate (negatively accelerate)

This means that the size and/ or the direction of the velocity will change

Newton's Second Law

Force = mass x acceleration

If the resultant force is non-zero, then the object must accelerate according to this formula.

SUVAT notation

a _____ is needed to make an object accelerate

resultant force

practice calculating the acceleration of these boxes

inertia

The tendency of an object to resist a change in motion - referred to as mass nowadays

Acceleration

Acceleration is the change in velocity over time

It is a vector quantity

There is an acceleration whenever there is a resultant force

Acceleration is measured in metres per second squared

This is written as m/s2 or ms-2 or m/s/s

A car accelerates from 4 m/s to 24 m/s in 5 seconds. What is the acceleration of the car?

4 ms^-2

A car accelerates from 4 m/s to 24 m/s in 5 seconds. What is the acceleration of the car?

15 m/s

An aircraft decelerates at 8 m/s2 for 6 seconds, from an initial velocity of 120 m/s. What is the final velocity of the aircraft?

72 m/s

A horse accelerates from 5 m/s to 17 m/s. The acceleration of the horse is 3 ms-2. For how many seconds was the horse accelerating?

4 seconds

mass

measures the number of atoms that something is made of and is the same everywhere in the universe

Weight

the pull of gravity on a mass and depends on the gravitational field strength g, so will be different up a mountain, on the Moon, in space…

They are connected using Newton 2

“g” is also called the acceleration due to gravity and is 9.8 N/kg or 9.8 m/s2 on Earth (or just 10 N/kg)

- A skydiver jumps out of a plane. The skydiver has a mass of 90 kg

- Just at the moment that they jump out of the plane, the only force acting on them is gravity

- After a few seconds, the air resistance force has increased to 360 N

- After a few more seconds the air resistance force becomes equal and opposite to the weight


1) Sketch these 3 situations as free-body diagrams

2) Calculate the acceleration in each case

3) Explain why the air resistance increases with time
(Take g = 10 N/kg)

A ball of mass 0.50 kg is moving horizontally to the right at a constant speed of 10 m/s

The ball hits a wall at right angles and rebounds with the same speed

The collision time is 0.20 seconds

Sketch this scenario

Does the ball accelerate?

Is there a resultant force on the ball?

Newton's Third Law

For every action there is an equal and opposite reaction

An interaction between two objects can be replaced by two forces, one acting on each object. These forces are equal in magnitude, but opposite in direction.

SUVAT equations

A student walks 200 m to a shop in a time of 50 seconds. They stop for 25 seconds then they return at a speed of 8 m/s back to the start along the same route
Plot this journey onto a displacement time graph

How far have they travelled?
What is their velocity in the first section?
What is their average velocity for the whole journey?
What is their average speed?

Total distance travelled:

400 meters (200 m to the shop and 200 m back).

Velocity in the first section:

4.0 m/s (they walked 200 meters in 50 seconds).

Average velocity for the whole journey:

0.0 m/s (since the displacement at the start and end is the same, the overall displacement is 0).

Average speed for the whole journey:

4.0 m/s (total distance of 400 meters divided by the total time taken for the journey).

Velocity-time graphs

On a velocity-time graph the area between the line and the x-axis is the displacement, the gradient is the acceleration

A rock, initially at rest, is dropped from a height of 2.0 m. At what time does the rock reach the ground?

A car accelerates in a straight line from 10 m/s to 30 m/s in a distance of 80 m. What is the acceleration of the car?

A motorcycle accelerates from 5 m/s for 6 seconds with an acceleration of 3 m/s^2

a) How far has the motorcycle travelled?
b) What is the final velocity of the motorcycle?

A plane goes from a velocity of 20 m/s to 80 m/s with an acceleration of 4 m/s^2 . How far has the plane travelled?

A 1 kg rock and a 2 kg rock are both dropped from a height of 10 m. Which one reaches the ground first?

A bullet is fired vertically up with a velocity of 200 m/s.
How high does the bullet get?
How high would it get on the Moon (g = -1.6 ms^-2)

Movement energy

Kinetic
Light
Thermal
Sound

stored energy

Gravitational
Elastic
Chemical
Nuclear
Magnetic
Electrical

energy

The ability to do work or cause change - the work done is the energy transferred

Gravitational Potential Energy

the work done when an object moves up (against the force of gravity) or down (with the force of gravity) is called gravitational potential energy

The GPE depends on the

change in height, h

gravitational field strength, g

mass, m

Kinetic Energy

Work needs to be done in order to get an object to a certain speed

The work done is called the kinetic energy and it depends on the

mass (in kg)

speed (in m/s)

Hooke's Law

Extension is directly proportional to force until the spring reaches it's elastic limit (Where k is the spring constant, which has units of N/m)

What is the unit for energy?

Joules (J)

Elastic potential energy

the energy of stretched or compressed objects

A student of mass 50 kg runs at 6 m/s
What is their kinetic energy?

900J

A car has a mass of 1200 kg and a speed of 30 m/s
A constant braking force of 5000 N is applied until the car stops

What is the stopping distance of the car?

What is the gravitational potential energy (GPE) of a 60 kg person if they are 100 m in the air? (take g=10 ms-2)

Give your answer in kilo-joules

What would the GPE be for the same height on the Moon? (g = 1.6 N/kg)

A car has a mass of 800 kg and a kinetic energy of 40 kJ
What is the speed of the car?

The car in the last question had a mass of 800 kg and a speed of 10 m/s
The speed of the car doubles

What happens to their kinetic energy? How many times bigger is it?

A skateboarder has a speed of 10 m/s and a kinetic energy of 2 kJ
What is the mass of the skateboarder (including the skateboard)?

A stone of mass 0.2 kg has 40 J of kinetic energy
What is the speed of the stone?