FORCES AND
ENERGY
CLASS 7 - UNIT 3
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Force is a vector
quantity
vector quantities are quantities
that possess both magnitude and
direction.
SPEED
Speed is the rate of change of position of
an object with time.
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Types of Speed
Uniform speed: A object is said to be in uniform speed
when the object covers equal distance in equal time
intervals.
Variable speed: A object is said to be in variable speed
when the object covers a different distance at equal
intervals of times.
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Average speed: Average speed is defined as the uniform
speed which is given by the ratio of total distance travelled
by an object to the total time taken by the object.
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Distance time graph
A distance-time graph shows how far an object has travelled in
a given time. It is a simple line graph that denotes distance
versus time findings on the
graph.
● Distance is plotted
On the Y-axis.
● Time is plotted
on the X-axis.
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Plot a graph describing a journey that has several parts to it, each
represented by a different straight line.
Part A: 09:00−11:00, the person travelled 3030 km away from their
starting point and that took them 22 hours.
Part B: 11:00−12:00, we can see that the line is flat, so the distance
from their starting point did not change – they were stationary.
Part C: 12:00−12:30, they moved a further 3030 km away from their
starting point.
Part D: 12:30−14:00, they travelled the full 6060 km back to where they
began.
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Textbook questions and
answers
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Turning Forces
1. if you apply a force to a spanner it
rotates. The pivot is at the bolt.
2. When you push open a door, you
apply a force to the edge of the
door furthest from the hinges.
This force has a turning effect on
the door
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The turning effect of a force is called the
moment of the force. Moments act about
a pivot in a clockwise or anticlockwise
direction.
https://www.youtube.com/watch?v=gr2XegnsxXM
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Moment of force = F x d
d is the distance from the fixed axis,
Moment of force is expressed in newton meter (Nm).
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Textbook questions and
answers pg 95
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PRESSURE
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Derivation for formula of pressure
Force increases pressure increases
Area increases pressure decreases
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P∝F
P∝ 1
A
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Textbook
questions
and
answers
pg 103
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PRESSURE IN LIQUIDS
Link https://www.youtub
e.com/watch?v=Cvp
6mLWbgaM
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Water pressure increases with depth because the water up above weighs down on
the water below.
Pressure can be measured in a variety of ways. Water pressure can be easily
calculated with a simple equation involving depth, density and gravity.
Pressure = Density ×Gravity ×Height
Pressure =ρ(rho)×g×h
Pressure in gases
Link https://www.youtub
e.com/watch?v=NzK
AJWTmlwg
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Gas pressure is caused when gas
particles hit the walls of their
container. The more often the
particles hit the walls, and the
faster they are moving when
they do this, the higher the
pressure. This is why the
pressure in a tyre or balloon goes
up when more air is pumped in.
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Link - https://www.youtube.com/watch?v=lgf1bPGFfYg
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Pressure and Temperature in
Gases
▪ Faster moving particles will
collide with the container
walls more frequently and
with greater force. This
causes the force on the
walls of the container to
increase and so the
pressure increases.
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TEXTBOOK
QUESTIONS
PG 110
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DIFFUSION
Process resulting from random motion of
molecules by which there is flow of matter from a
region of high concentration to a region of low
concentration.
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Diffusion in gases
when a sample of gas is introduced to one part of a closed
container, its molecules very quickly disperse throughout
the container from high concentration to low
concentration.In a closed environment, diffusion will
ultimately result in equal concentrations of gas throughout.
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Diffusion in liquids
Diffusion can also
happen in liquids. This is
because the particles in
liquids can move around
each other, which
means that eventually
they are evenly mixed.
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TEXTBOOK QUESTIONS
AND CHECK YOUR
PROGRESS
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THANK YOU !
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"Don't let what you cannot do
interfere with what you can do." —
John Wooden