FORCES AND MOTION (1)

VELOCITY AND ACCELERATION

Formula linking

• average speed

• distance moved

• time taken

Average speed = distance moved / time taken

VELOCITY AND ACCELERATION

What is the difference between speed and velocity

• speed is how fast your going

• velocity must also have the direction specified

VELOCITY AND ACCELERATION

What is acceleration?

• how quickly velocity is changing

• A change in velocity can be due to either a change is speed or a change in direction or both

• the unit of acceleration is m/s²

VELOCITY AND ACCELERATION

Formula for acceleration?

acceleration = change in velocity / time taken

DISTANCE - TIME GRAPHS & VEOCITY TIME GRAPHS

Distance time graphs

What does the … tell us:

• gradient

• flats sections

• steep sections

• curves

• a curve getting steeper

• levelling of curve

Gradient

• at any point gives us the speed of the object

Flat sections

• where it has stopped

Steep sections

• going faster

Curves

• represent acceleration

A curve getting steeper

• speeding u

A levelling off curve

• slowing down

DISTANCE - TIME GRAPHS & VEOCITY TIME GRAPHS

Distance time graphs

How do you calculate the average speed over a period of time

Total distance / time taken

DISTANCE - TIME GRAPHS & VEOCITY TIME GRAPHS

Velocity time graphs

What does the … tell us:

• Gradient

• Flat sections

• uphill sections

• down hill sections

• area under the graph

• curve

Gradient

• acceleration

Flat sections

• steady speed

uphill sections

• sections are acceleration

downhill sections

• sections are deceleration

Area under the graph

• the distance travelled in that time interval

Curve

• changing acceleration

MASS, WEIGHT AND GRAVITY

GRAVITY

what is gravity

• the force if attraction between all masses

MASS, WEIGHT AND GRAVITY

GRAVITY

What is its 3 effects

1. on the surface of a planet, it will make things accelerate towards the ground

2. it gives everything weight

3. it keeps planets, moon and satellites in their orbits - the orbit is a balance between the forward motion of the object and the force of gravity pulling it inwards

MASS, WEIGHT AND GRAVITY

MASS

What is it

• the amount of matter in a object

• every given object will have a mass

• an object will have the same mass whether it is on earth or the moon

• measured in kilograms with a mass balance

MASS, WEIGHT AND GRAVITY

WEIGHT

What is it

• is caused by the pull of gravity

• it is normally the force of gravity pulling something towards the centre of earth

• Differing to mass an object will have a different weight, on the moon (less) as the force pulling on it is less

• measured in newtons, using a spring balance or a newton meter

MASS, WEIGHT AND GRAVITY

Formular linking

• weight

• mass

• gravitational field strength

Weight = mass x gravitational field strength

FORCES AND FRICTION

The types of force

• WEIGHT

  • acts straight downwards

• REACTION FORCE

  • acts perpendicular to a surface away from it

• ELECTROSTATIC FORCE

  • between 2 charged objects

• THRUST

  • push or pull

• DRAG

  • slowing something down

• LIFT

• TENSION

FORCES AND FRICTION

Friction

The 3 types of friction

1. Friction between solid surfaces which are gripping

2. Friction between solid surfaces which re sliding past each other

3. resistance or drag from fluids

FORCES AND FRICTION

Friction

Resistance or drag from fluids

• the most important factor is keeping the shape of the object streamlined (e.g. deflectors make large vehicles more streamlined to reduce drag

• in a fluid, friction always increases as the speed increases

INESTIGATION MOTION

Toy car on ramp

(practical)

1. set up your apparatus

2. mark a line on the ramp, so they car sets off from the same point

3. measure the distance between each light gate

4. let go of the car just before the light gate so that it will start to roll down the slope

5. the light gates should be connected to a computer, so when the car passes through each light gate, a beam on light is broken and a time is recorded by data-logging software

6. repeat this at least 3 times and get an average time it takes for the car to reach each gate

7. divide the distance between the light gates by the time taken to get an average speed

3 LAWS OF MOTION

1st law

• balanced forces mean no change in velocity

• if all the forces on an object are balanced, then it will stay still

• is the object is moving it will carry on at the same velocity

3 LAWS OF MOTION

2nd law

• a resultant force means acceleration

• if there is an unbalanced force the object will acceleration in the direction with the greater force

• Acceleration can take 5 different forms:

  • starting

  • stomping

  • speeding up

  • slowing down

  • changing direction

3 LAWS OF MOTION

2nd law

formular linking:

• force

• mass

• acceleration

force = mass x acceleration

COMBINING FORCES

what is the difference between vectors and scaler quantities

Scaler

• only has magnitude

Vectors

• have magnitude and direction

COMBINING FORCES

How to work out the resultant force

• you need to combine vectors

• chose a positive direction, add any forces up in that specified direction then subtract any forces in other directions

TERMINAL VELOCITY

What is a terminal velocity

• when an objects starts to fall, it has more force accelerating it than resistance slowing it down

• as the velocity increases the resistance builds up

• the resistance force gradually reduces the acceleration until eventually the resistance force is equal to the accelerating force.

• at this pint the object will not be able to accelerate anymore as it will have reached its maximum or terminal velocity

TERMINAL VELOCITY

Depends on the objects shape and area

• air resistance causes objects to fall at different speeds and the terminal velocity of any object is determined by its drag compared to its weight

HOOKES LAW

what is it

• the force exerted on a string is directly proportional to its extension

HOOKES LAW

Investigation with a spring

(Practical)

• set up the apparatus, make sure you have spare masses and measure the weight of each with a balance

• measure the length of a spring (with an accurate mm ruler), when no load is applied, ensure the ruler is vertical and being measured at eyelevel

• add one mass at a time and allow the string to come to rest, them measure the new length

• repeat this process until you have enough measurements at least 3 times

• calculate an average value for the length of the spring for each applied weight

• plot the results on a graph

• it should show that the increase in weight on the spring leads to the same increase in extension

HOOKES LAW

Hooke’s law stops working when the force is great enough

• when the force become great enough the graph will start to curve

• as if you increase the force past this point the material will become permanently stretched

STOPPING DISTANCE

factors that affect the total stopping distance

stopping distance it takes is divided into:

1. thinking distance

2. breaking distance

STOPPING DISTANCE

Thinking distance

1. how fast you are going

   • the faster you’re going the further you’ll go

2. your rection time

   • affected by tiredness, drugs, alcohol and old age and inexperience

STOPPING DISTANCE

Breaking distance

1. how fast you’re going

   • the faster you’re going the further you will go

2. mass of the vehicle

   • with the same breaks, the vehicle with the larger mass will take longer to stop

3. how good the brakes are

   • must be checked and maintained regularly

4. how good the grip is

   • this depends on:

     1. road surface

     2. weather conditions

     3. tyres