This page contains the detailed and easy notes for GCSE OCR Physics Forces for revision and understanding Forces.
GCSE OCR FORCES COMPLETE REVISION SUMMARY
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FORCES
FORCES
- 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:
BBC Bitesize
Wikipedia
Wikimedia Commons
Image Source:
Wikipedia
Wikimedia
Commons
Flickr
Pixabay
Make sure you have watched the above videos and are familiar with the key definations before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well.
Forces In Action
- Acceleration 1 MS
- Acceleration 1 QP
- Acceleration 2 MS
- Acceleration 2 QP
- Acceleration 3 MS
- Acceleration 3 QP
- Distance & Displacement MS
- Distance & Displacement QP
- Distance-Time Relationship 1 MS
- Distance-Time Relationship 1 QP
- Distance-Time Relationship 2 MS
- Distance-Time Relationship 2 QP
- Distance-Time Relationship 3 MS
- Distance-Time Relationship 3 QP
Motion
- Newton’s First Law MS
- Newton’s First Law QP
- Newton’s Second Law 1 MS
- Newton’s Second Law 1 QP
- Newton’s Second Law 2 MS
- Newton’s Second Law 2 QP
- Newton’s Second Law 3 MS
- Newton’s Second Law 3 QP
- Newton’s Third Law MS
- Newton’s Third Law QP
Force And Motion
- Moments, Levers and Gears 1 MS
- Moments, Levers and Gears 1 QP
- Moments, Levers and Gears 2 MS
- Moments, Levers and Gears 2 QP
- Moments, Levers and Gears 3 MS
- Moments, Levers and Gears 3 QP,
- Momentum 1 MS
- Momentum 1 QP
- Momentum 2 MS
- Momentum 2 QP