GCSE OCR 21st Century Physics Explaining motion Complete Revision Summary

This page contains the detailed and easy notes for GCSE OCR 21st Century Physics Explaining motion for revision and understanding Explaining motion.

GCSE OCR 21st Century Physics Explaining motion Complete Revision Summary

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Explaining motion

Explaining motion

  • Scalar and vector Quantites
  • Contact and non – contact Forces
  • Gravity
  • Resultant Forces
  • Work Done and Energy transfer
  • Forces and Elasticity
  • Moments, Levers and Gears
  • Pressure in a Fluid
  • Atmospheric pressure

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FORCES AND MOTION

Distance and Displacement Speed, Velocity, Acceleration Distance Time Graph Velocity Time Graph

NEWTONS LAW OF MOTION

Newtons First Law

Newtons Second Law

Newtons Third Law

Forces and Breaking

Breaking Distance

Thinking Distance

Reaction Time

MOMENTUM

Momentum

Conservation of Momentum

         SCALARS AND VECTORS

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DISTANCE AND DISPLACEMENT

  • Distance is scalar Quantity
  • Displacement is a vector Quantity
  • Displacement is speed in a given
    direction

CONTACT AND NON CONTACT FORCES

Force is push or pull on an object that causes an object due to
interaction with another object that causes an object to:-

a) change speed
b) Change direction
c) change shape

FRICTION FORCE

It is a necessary evil

Friction is a contact force that opposed motion between the
two surfaces that are in physical contact.

  • It is a resistive force
  • It happens in the opposite direction of motion.

a) It helps to light a matchstick.

b) The friction between the tyres and the
roads prevent the vehicle to slide.

a) It can cause wear and tear of machines

b) It can cause wear and tear of tyres

NEWTONS THIRD LAW OF MOTION

THE SKATERS MOVE TOWARDS EACH OTHER
AS THEY PULL ON EACH OTHER WITH EQUAL
AND OPPOSITE FORCE

RESULTANT FORCES

Net force = 0 N ( forces are balanced)
The body will stay at rest

It is the total force that acts on the body. It is the sum
of all the forces that acts on the body .

The resultant force decides the speed and the direction
of the body.

BALANCED

If the resultant force is zero

  • If the forces are balanced and
    the body is at rest then it will
    stay at rest.
  • If the forces are balanced and the
    body is moving it will keep on moving
    with the same speed and direction

UNBALANCED

If the resultant force is
non zero

The body will
move in the direction
of resultant force.

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NEWTONS FIRST LAW OF MOTION

If an object is at rest it will remain at rest
If an object is in motion it will continue to move with the same
speed and direction unless no resultant force acts on it.

If the resultant force is non zero or unbalance the object will
move or change speed or direction.

MOMENTS

It is the turning effect of force.

MOMENT =. Force. X Perpendicular distance
from the pivot

Nm   =    Nxm

Greater distance from the pivot increases
the moment or the turning effort
so a small effor can lift a heavy load.

MOMENT QUESTIONS

Moment = Force X distance
= 30 X 10
= 300 Nm

Q2 The moment of a spanner is 50 Nm.
Calculate the force acting at a distance of
10m from the pivot.

LEVERS AND GEARS

Simple Lever and Force Multipliers

In all these levers, the turning effect of force is greater by increasing the distance of effort
further away from the pivot. It increases the turning effect and multiply the force with a
small effort.

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GEARS

GEARS TRANSMIT TURNING EFFECT OF
FORCE

  • Gear A Connected to the engine
  • Smaller radius

GearB

  • Bigger radius
  • Connected to Wheels

At the Point of Contact they exert equal and opposite force.

Turning effect is greater due  to greater radius .

Low gear

  • Low speed and high turning
    effect
  • small gear wheel run a bigger
    gear wheel
  • bigger wheel has greater turning
    effect but slow speed

High Gear

  • High speed and
    low turning effect
  • large gear wheel run
    a smaller gear wheel
  • small gear wheel force
    acts near to the shaft it
    run faster with a high speed
    but lower turning effect

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MOMENTS AND EQUILBRIUM

The sum of clockwise moments=
The sum of anticlockwise moments

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WEIGHT OF THE BEAM

CENTRE OF MASS

It is the point at which the entire mass of the object
can be thought as being concentrated.

CENTRE OF MASS FOR SYMMETRIC OBJECTS

  • It is along the point of symmetry
  • If there more line of symmetry the centre of mass
    is at the intersection of lines of symmetry

SUSPENDED OBJECT

  • The center of mass is directly below the point of suspension.
  • When suspended, the weight will give the turning effect and
    it will come back to its equilbrium position

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SPEED, VELOCITY AND ACCELERATION

Q1 A car is travelling at the speed of 20 m/s.
Calculate the distance covered in 10 minutes

DISTANCE TIME GRAPHS

VELOCITY TIME GRAPHS

SLOPE OF VELOCITY TIME GRAPH= ACCELERATION

AREA UNDER THE GRAPH = DISTANCE

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EQUATIONS OF MOTION

NEWTONS SECOND LAW OF MOTION

The acceleration of a body is

a) directly proportional to the resultant force
b) inversely proportional to the mass of an object

NEWTONS SECOND LAW OF MOTION

F = Mass x acceleration

SPEED UP

  • The velocity of the object increases.
  • The object accelerated.
  • The resultant force is in the direction of motion.

SPEED DOWN

  • The velocity of the object decreases .
  • The object is decelerated.
  • The resultant force is opposite to the direction of motion.

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WEIGHT AND TERMINAL VELOCITY

Weight (N) =  Mass (Kg) x GRAVITATIONAL FIELD
STRENGTH (N/Kg)

g on earth  = 9.8 N/Kg

or  10 N/Kg

FORCE AND WORK RELATIONSHIP

Q1 Calculate the work done when the force of 100 N moves the object
to a distance of 2m ?

W =F x S

= 100 x 2

= 200J

Q2 Calculate the force applied when 100 J of work is done to move
an object to a distance of 5 m ?

TERMINAL VELOCITY

It is the constant velocity of an object when
the resultant force is zero and the weight
of the body is balanced by the drag and
body has zero acceleration.

Terminal Velocity

TERMINAL VELOCITY IN FLUIDS

  • In fluids, weight of the object is balanced by frictional force acting
    upwards.
  • The body falls with constant velocity as net force or resultant force
    acting on the object is zero, so the body falls at constant velocity
    called the terminal velocity.

FORCES AND BREAKING

STOPPING DISTANCE

  • The shortest distance a vehicle
    can safely stop in.
  • It is the sum of thinking distance
    and braking distance.

THINKING DISTANCE

The distance travelled by the body
during its reaction time.

= Speed x reaction time

Affected by tiredness, drug, alcohols
as all these affects the reaction time.

BRAKING DISTANCE

  • Distance travelled by the body when
    the braking force is applied.
  • Poor weather conditions, road conditions,
    poorly maintained vehicles, speed of
    the vehicle and the mass of the vehicle
    affects the same.

MOMENTUM

Principle of conservation of momentum

  • Momentum is a vector quantity .
  • It has a magnitude as well as direction.
  • Greater the speed, greater the momentum.
  • Higher the velocity, higher the momentum.

CONSERVATION OF MOMENTUM

IMPACT FORCES

Relationship between force and momentum

If we increase the time and the momentum is conserved,
the impact force can be decreased.

So greater impact time = reduced impact force

CAR SAFETY FEATURES

All these features increases the impact time, decreasing the momentum and thus
reduced the impact force.

FORCES AND ELASTICITY

Effect of force on elastic objects:-

Change shape or deformation by

  • Bending
  • Stretching
  • Compressing

Elastic Deformation

Object regains its original shape when
the force is removed like stretched rubber
band.

Inelastic Deformation

Object that does not gain its original shape
and changes shape permanently.
Example: overly stretched rubber.

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FORCES AND ELASTICITY

HOOKE’s LAW

Force on a spring is directly proportional
to the extension until it reaches its
limit of proportionality.

FORCES AND ELASTICITY

SPRING CONTSTANT

It is the measure of the stiffness of the spring.
Greater the spring constant stiffer is the object.

LIMIT OF PROPORTIONALITY

It is the point upto which the springs obeys
Hooke’s law. Beyond this point, the object
comes in the plastic region and no longer
obeys the Hooke’s law.

Q1 Calculate the force applied on the spring when
it is extended by 2m. The spring constant is 5N/m

F  =  k e

=5 x  2

=10 N

Q2 Calculate the spring constant of a spring when a force
of 50N extends the spring by 5 m.

K  F/e

=50/2

=10 N/m

ELASTIC POTENTIAL ENERGY

E =1/2 k e 2

E = Elastic potential energy (J)

K = spring constant (N/m)

e= extention in the spring (m)

Elastic potential energy is the
energy stored in the spring when
it is stretched or compressed.

PRESSURE

  • Greater the force greater the pressure .
  • Smaller the area more will be the pressure exerted.

PRESSURE IN LIQUIDS

ATMOSPHERIC PRESSURE

  • Atmospheric pressure arises due to
    collission of the airparticles with the
    Earth’s surface.
  • It decreases with altitude as the number
    of particles decreases with height
    causing decrease in weight.

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KEY TERMS

a) Forces :-Force is push or pull on an object that causes an
object due to
interaction with another object that causes an
object to:-
a) change speed
b) Change direction
c) change shape

b) Scalar :-Quantity that has magnitude only.
eg Length, Area, Volume etc .

c) Vector : Quantity that has magnitude
as well as direction. eg Displacement,
velocity, acceleration, momentum.

d) Friction :Friction is a contact force that opposed motion
between the
two surfaces that are in physical contact.

e) Newton First Law of Motion :-If an object is at rest it will remain at rest
If an object is in motion it will continue to
move with the same
speed and direction unless no resultant force
acts on it.

f) Newton Second Law of Motion:- The acceleration of a body is
a) directly proportional to the resultant force
b) inversely proportional to the mass of an object.

g) Newton Third Law of Motion:-For an every action force, there is an
equal and opposite reaction force.

h) Resultant Force It is the total force that
acts on the body. It is the sum
of all the forces that acts on the body .The
resultant force decides the speed and the
direction
of the body.

i) Free Body digrams are the graphical
illustration to represent all the forces
acting on a body.

j) Moments: It is the turning effect of force. It
is calculated by force multiplied by the
perpendicular distance from the pivot.

k) Levers : In all these levers, the turning
effect of force is greater by increasing the
distance of effort
further away from the pivot. It increases the
turning effect and multiply the force with a
small effort.

l) Gears : GEARS TRANSMIT TURNING EFFECT OF
FORCE.

m)Centre of Mass: It is the point at which the
entire mass of the object
can be thought as being concentrated.

n) Speed: It is the distance travelled divided by
the time taken.

o) Velocity: Speed in a given direction.

p) Acceleration: It is the change in speed over
time taken.

q)Weight: It is the force acting on the body due to gravity.

r) Terminal Velocity: It is the constant velocity
of an object when
the resultant force is zero and the weight
of the body is balanced by the drag and
body has zero acceleration.

s) Thinking Distance: The distance travelled by
the body during its reaction time.

t) Breaking Distance: Distance travelled by the
body when the braking force is applied.

u)Momentum: It is the product of mass and
velocity.

v) Conservation of Momentum: In a closed system,
the momentum before
the collission and after the collission remains
unchanged.

w) Hooke’s Law: Force on a spring is directly
proportional
to the extension until it reaches its
limit of proportionality.

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Disclaimer:
I have tried my level best to cover the maximum of your specification. But this is not the alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.

References:

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