FORCES AND MOTION

define velocity

speed of an object in a specific direction

define acceleration

rate of change of velocity

(can be speed or change)

define mass

how much matter an object contains

define weight

the force an object experiences in gravitational field

define force

push or pull on an object due its interaction with another object

define gravity

force of any two objects that has mass

why can an aeroplane change direction at constant speed

changing its velocity

define reaction force

force exerted on an object by the surface it is resting on, acts at right angle

what does gradient in DISTANCE TIME GRAPH represent

speed of object

what do flat sections show in DISTANCE TIME GRAPHS

object has stopped

what does a curve getting steeper show in DISTANCE TIME GRAPH

speeding up (increasing gradient)

how to work out gradient in DISTANCE TIME GRAPH

1. y / x

2. Y is DISTANCE (m), X is TIME (s)

what does gradient show in VELOCITY-TIME graph

acceleration

what do flat bits represent VELOCITY-TIME GRAPH

object at constant velocity

what does area underneath VELOCITY-TIME graph show

distance travelled in that time

3 important effects of gravity

1. on surface of every planet, gravity makes things accelerate towards ground at 10 m/s²

2. gives everything weight

3. keeps moon, planets, satellites in their orbits

→ orbit is balance between forward motion of object + gravity pulling it inwards

why does mass weigh less on the moon

• force of gravity pulling on it is less

7 types of force

NEED TO DO

4 contact forces

1. friction

2. air resistance

3. reaction force - if rock (has mass) on table, must be equal + opposite reaction force

4. tension (pull exerted through rope)

3 non contact forces

1. gravitational

2. electrostatic, between two charged objects

3. magnetic, between objects with magnetic poles

what does is friction

• a force that opposes motion

3 main ways friction occurs:

1. between two solid surfaces that are gripping

2. two solid surfaces sliding past each-other

→ can be reduced by lubricant such as oil/grease

3. ‘drag’ - when an object moves through a fluid( gas or liquid)

→ can be reduced by keeping shape of object streamlined

what is newtons first law?

if all forces acting on an object are balanced, it will stay still or continue moving with same velocity

→ must be zero resultant force

what is newtons second law

if there is an unbalanced force, the object will accelerate in that direction

→ no steady speed

how to work out overall effect of forces along same line

• add or subtract them

• overall force + resultant force

vector vs scalar quantities

• 4 examples each

vector: magnitude AND direction

scalar: ONLY magnitude

VECTOR:

• force

• weight

• velocity

• acceleration

SCALAR:

• mass

• temp

• time

• length

what is stopping distance

distance covered in the time between driver spotting a hazard and coming to a complete stop

what is thinking distance

distance between car noticing hazard and braking

(while driver reacts)

what is stopping distance

distance car travels during deceleration whilst brakes are applied

(while braking)

2 factors of thinking distance

1. speed

2. reaction time:

• tiredness

• drugs

• disraction

• old age

4 factors of braking distance

1. speed

2. mass of vehicle

3. condition of brakes

4. the grip:

• road surface

• weather conditions

• tyres

what is Hookes law

extension is directly proportional to the force applied, up to its limit of proportionality of an elastic object

what happens if weight attached to wire

wire stretches, weight pulls down with force producing equal and opposite forces

Y and X axis for Hookes law

Y is force

X is extension

when does hookes law stop working

when force becomes great enough

what is elastic limit

if force increased past elastic limit, material becomes permanently stretched, will remain after force removed

what does it mean if an object can return to og shape after elastic deformation

displays elastic behaviour

TERMINAL VELOCITY