IGCSE Edexcel Physics forces key terms DA - JAM

What is a force

A push or a pull

What effect can a force have on an object

Change speed
Change direction
Change shape
Change size

What are forces measured in and by

Newtons
Newtonmeter

Gravitational force

A force exerted between bodies because of their mass and the strength of the gravitational field (g)

Weight

Gravitational force of the earth on an object. Weight = mass x gravitational field strength

Normal reaction

The repulsive force that stops two touching bodies moving into each other
Force acts at 90 degrees to the surface of the body

Friction

Force that opposes motion when two surfaces/objects are in contact.

Air resistance/drag

Frictional force that opposes the movement of objects through the air

Upthrust

Force experienced by objects when placed into a fluid to the displacement of the fluid they are in.

magnetic force

Force between magnets and for ferromagnetic objects in a magnetic field

Electrostatic

Attractive and repulsive forces due to bodies being charged

Vector

Have direction and magnitude e.g. Velocity and force

Representing vectors

Arrowed straight line is used
Arrow indicates direction and length is proportional to the magnitude

Scalar

Not have a direction eg mass, speed (still units and magnitude)

How to work out the stopping distance of a car

Thinking distance + breaking distance

What affects the thinking distance

Speed
Alcohol
Drugs
Tiredness
Distractions
Reaction time

What affects the breaking distance

Speed
Car mass
Conditions of road
Brakes or tyre conditions

Thinking distance

The distance travelled by a car in the time it takes the driver to react.

Breaking distance

The distance your car travels after you apply the breaks

What happens immediately after a sky diver jumps out of the plane?

Weight is greater than air resistance, resultant force so object accelerates

What happens after the sky diver has been falling for a bit?

Weight equals air resistance, so forces balance and no resultant force. This means it travels at a constant speed (terminal velocity)

What happens when a sky diver opens the parachute?

The weight is less than air resistance so there is a resultant force upwards and deceleration occurs

What happens finally when a sky diver is near the ground?

The weight is equal to air resistance again so no resultant force and therefore terminal velocity (but at a lower speed)

Hookes law

The extension of a spring is directly proportional to the force applied

What materials follow hookes law?

Spring, metal wire, marshmallows, ...

What does hookes law graph look like

Linear region is hookes law
Goes through the origin
Directly proportional

What does the elastic limit mean

After it, the spring won't return to original shape once load is taken over (behaves plastically)

What doesn't obey hookes law

Elastic band
S shape graph but does return to original length

Hookes law practical

Measure original length of the spring
Add masses of 1N
Measure extended length
Repeat for different masses
Calculate the extension = extended length - original length

Newton's first law of motion

An object is stationary or moving at a constant velocity unless acted on by a resultant force.

Newton's second law of motion

Resultant force = mass x acceleration.
F=ma

Third law of motion

If object A exerts a force on object B then object B exerts the an equal and opposite force on object A

Speed

distance/time

Velocity

Speed in a given direction.
Example: The boy was running at 5 m/s North

What does the gradient of a distance-time graph represent?

speed

If the gradient of a distance-time graph is flat, what does this mean?

Object is stationary (not moving)

What is the definition of acceleration?

acceleration = change of velocity/time taken

What does the gradient of a velocity-time graph represent?

Acceleration

What does the area under a velocity-time graph represent?

Distance travelled

If the gradient of a velocity-time graph is flat, what does this mean?

Acceleration is zero, travelling at a constant velocity