Physics : P5

Define a force.

A push or pull acting upon an object: caused by it interacting with something

What are the contact and non-contact forces?

Contact = normal contact force, friction, tension, air resistance

Non-contact = gravity, electrostatic, magnetic

Define a vector and give examples

A quantity with a magnitude (size) and direction

Force, velocity, momentum, displacement and acceleration

Define a scalar and give examples

A physical quantity with a magnitude and no direction

Temperature, mass, time, distance, speed

What is an interaction pair?

A pair of forces that are equal and opposite and act on two interacting objects

Define acceleration

How quickly the velocity (speed or direction) is changing.

What is the formula for acceleration and deacceleration?

Acceleration = change in velocity/time taken

M/s(squared) = (m/s) / (s)

A = △v/t

(DEACCELERATION IS THE SAME BUT THE ANSWER WILL BE A NEGATIVE)

Define uniform acceleration

Consistent, not changing velocity

Acceleration due to gravity on Earth is…

9.8 m/s(squared)

Define resultant force

The overall force acting upon an object

What is the equation for resultant force?

Resultant force = biggest force - other forces

What does the resultant force determine? What if its 0?

The direction an object moves

The object us at constant velocity

Define acceleration and deacceleration

Acceleration = velocity increasing

Deaccleration = velocity decreasing

Define mass and its units

A measure of the number of atoms in an object

Kg

Define weight and its units

A force called by the pull of gravity on mass

Newtons (N)

Define gravitational field strength

Acceleration of an object caused by gravity (9.8 N/Kg on Earth)

Define gravity

A force of attraction between masses determined by mass and distance

What is the formula for weight?

Weight = mass x gravitational field strength

N = Kg x N/Kg

Define displacement and an example

A vector quantity which measures distance and direction in a straight line from start to end point.

E.g. if you work 5m north then 5m south, displacement = 0m, direction = 10m

Define speed and how it is calculated

A measure of how far an object travels in a given time

Speed = distance/time

What is the speed of someone walking, running and cycling?

Walking = 1.5 m/s

Running = 3 m/s

Cycling = 6 m/s

What is the speed of a car, train, plane?

Car = 25 m/s

Train = 30 m/s

Plane = 250 m/s

Define work done and how it is calculated

When energy is transferred and a resultant force moves an object, it is only done when a force is applied.

Work done = force x distance

J = N x m

1J of work done equates to…

1J of work done is when a force of 1N causes an object to move by 1m

Define terminal velocity

When the frictional and accelerating force are equal terminal velocity is reached and the object falls at a steady speed.

What 2 factors impact terminal velocity?

• Less streamlined = lower TV

• Large SA = lower TV

What is Newton’s first law?

Objects at rest and objects in motion remain in motion in a straight line, unless acted upon by an unbalanced force.

What is Newton’s second law?

Forcé = Mass x acceleration

What is Newton’s third law?

For every action there is an equal and opposite reaction.

Define inertia

An object continuing in the same state of motion

Define inertial mass

How difficult it is for an object to change its velocity

Define momentum and its formula

A property of moving objects. The greater the mass and velocity of an object the greater the momentum/

Momentum = mass x velocity

P = m x v

(Kg m/s) = (Kg) x *m/s)

What is conservation of momentum?

In a closed system the total momentum before an event (collision) is equal to the total momentum after the event.

What is the formula for total momentum?

M1 x V1 = M2 x V2

Mass object 1 x velocity object 1 = mass object 2 x velocity object 2

Kg x m/s = Kg x m/s

What is the equation that links initial velocity, final velocity, acceleration and distance?

Final velocity² - initial velocity² = 2 x acceleration x distance

V² - u² = 2 x a x s

M/s - m/s = 2 x m/s² x m

If initial velocity is not given use..

0: the object starts stationary

What is the formula for reaction time?

Reaction time = √2 x acceleration x distance / acceleration

T = √2as / a

S = √2 x m/s x m / m/s²

Define friction? What does it cause?

A resistive force that slows things down and tries to stop objects sliding past each other, acting in the opposite direction to an objects moving.

It causes the wearing down of surfaces due to the release of thermal energy.

Define lubricants

Used to reduce friction in machinery and protect surfaces

Define air resistance

Friction caused by an object moving through the air

Define drag

Friction caused by an object moving through liquid

Define stopping distance and how its calculated

The total distance covered in the time taken from a driver seeing a hazard to stopping

Stopping distance = thinking distance + braking distance

Define thinking distance

The distance the vehicle travels during the drivers reaction time from the spotting of a threat

Define braking distance

The distance a vehicle travels once brakes are pressed

What factors impact thinking distance?

Reaction time, drugs, alcohol, speed, velocity

What factors impact braking distance?

Tyre conditions, speed, weather, brake conditions

As speed doubles breaking distance….

As speed trebles breaking distance…

Increases by + 2²

Increases by + 3²

Label each point on the distance, time graph

A = constant speed

B = stationary

C = faster constant speed

D = constant speed (return)

Label each point on the speed/velocity , time graph

A = gradual acceleration

B = steady speed

C = steady acceleration

D = steady deacceleration

Define elastic deformation

When an object goes back to its original shape and length after the force has been removed. Epe —> Ke

Elastic deformation can only happen when…

An object has energy in its elastic potential store

Define inelastic deformation

When an object can not return back to its original shape due to the force applied.

What formula links force, spring constant and extension?

Forcé = spring constant x extension

N = N/m x m

What is the formula for elastic potential energy?

Epe = ½ x spring constant x extension²

J = ½ x N/m x m²

What does the curve represent?

Limit of proportionality, elastic limit: object is inelastically deformed