Describing motion
Displacement is distance moved in a specific direction
1.
2.
3.
4.
5.
6.
Steady speed
Steady speed
Stationary
Decreasing speed
Increasing speed
Stationary
Note: gradient of a
distance time graph
gives you the speed
1. Constant
acceleration
2. Constant
deceleration
3. Steady speed
4. Decreasing
acceleration
5. Increasing
acceleration
6. Stationary
Note:
Gradient of a
velocity time
graph gives
you the
acceleration
Speed-time graphs
To get the distance covered from a velocity-time graph we calculate
the area under the graph.
Common shapes include rectangle, triangle and trapezium.
Area of rectangle =
Area of triangle =
Area of a trapezium =
For curved graphs we use the method of counting the squares to estimate the distance covered.
Calculate the deceleration of the vehicle
Deceleration = ………………………….………………………. [2]
a) Calculate the total distance covered by the vehicle.
b) Find the average speed of the car.
VECTORS AND SCALARS
Vector quantities are described by magnitude and direction
Scalar quantities have only magnitude.
List five vector quantities you know
RESULTANT OF A VECTOR
Vector addition
Parallelogram law (scale drawing)
List five scalar quantities you know
Force is a pull or push. Measured in newton using a force meter
Forces can cause things to change shape, volume, direction of motion, speed or state of motion.
Newton’s laws of motion
Example: A body of mass 5kg is acted upon by a force and its speed increases from 10m/s to 30m/s
in 4s. calculate the resultant force acting on the body.
FALLING OBJECTS
Bodies experiencing free fall have acceleration due to gravity. Downwards this value is 10m/s2 on
earth and upwards it has a value of -10m/s2.
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Terminal speed = 40m/s
At terminal velocity, the air resistance
equals to the weight meaning
resultant force equals zero.
From A to B the body is having a
decreasing acceleration
At point B a parachute is opened and
the air resistance is greater than the
weight which makes the body to
decelerate downwards.
The new terminal speed is 5m/s and
at that speed the air resistance and
the weight are once again equal.
MOVING IN CIRCLES
When an object is moving in a circular track, a force directed towards the centre of the path keeps it
in the track. This force is the centripetal force.
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Speed is constant
Velocity is changing –observe the direction changing
The centripetal force is the resultant force
Acceleration is directed towards the centre of the
path.
The centripetal force is given by the relation
Mean it is proportional to the square of the velocity
and the mass
The force is also inversely proportional to the radius
of the orbit.
Momentum and collision
Momentum is the product of mass and velocity
Unit: kgm/s and it’s a vector quantity.
HOOKE’S LAW
It states that the extension in a spring is directly proportional to the force provided the elastic limit
of the spring is not exceeded.
Extension
force
Where
F = force/load
force constant
X= extension
where
new length
original length
The point where the
spring stops to obey
Hooke’s law is the
proportional limit or
elastic limit.
A. Springs are connected in series. The
total extension is the sum of the
extensions
B. Springs connected in parallel. The
total extension is found by
Question
A spring of length 12cm is loaded with a load of 15N and its length increases to 12.5cm.
a) Calculate the force constant of the spring
b) Find the new length if the spring is loaded with a force of 17.5N
c) What force will stretch the spring to a new length of 14.8cm? State any assumption you
made.
THE LAW OF MOMENTS
It states that the sum of clockwise moments about a point is equal to the sum of anticlockwise
moments about the same point.
Clockwise moments =
Anticlockwise moments =
)
For equilibrium the following two conditions must be satisfied
1. Resultant moment must be equal to zero. (clockwise moments is equal to the
anticlockwise
2. The resultant force must be equal to zero. ( sum of upward forces = sum of downward
forces)
There are three types of equilibrium: stable, unstable, and neutral
Stable equilibrium- object returns to its original shape after slight displacement
Unstable equilibrium- object moves away from its original position after slight displacement
Neutral equilibrium- object is independent of displacements from its original position.
Write brief notes on the following types of forces
a) Gravity force
b) Electrostatic force
c) Magnetic force
d) Centripetal force
e) Friction force
f)
Tension forces
g) Compression forces
PRESSURE
Is the force acting normally per unit area
Unit = Pascal (Pa)
1Pa =
1N/m2
Generally,
REMEMBER:
FORCE =WEIGHT(W) =
Show working here…
Explain your reasoning here
Pressure in liquids
Pressure in liquids depends on density of the liquid, depth and the acceleration due to gravity.
Generally, liquid pressure = density
gravity
depth
Or
Also note the following additional properties of liquid pressure
a) Pressure at the same level is equal
b) Pressure in liquids distributes equally in all directions. This is because liquids are
incompressible. This property is applied in hydraulic machines.
PRESSURE IN GASES
a) Atmospheric pressure
Defined as the pressure exerted due to the weight of air in the atmosphere
Atmospheric pressure has a value of 76cmHg or 760mmHg and is measured using a mercury
barometer at sea level.
1 atmosphere (atm) =76cmHg = 100,000 Pa (approx)
The mercury barometer
The atmospheric pressure will be equal to the
height of the mercury in the capillary tube above
that in the bulk liquid or beaker.
It will be 760mmHg at sea level.
Question
Change 88cm of mercury to Pascals.
B) Measuring pressure of a gas trapped in a container
The U tube manometer
The gas is connected to one end of the
tube and the other end is left open to
atmospheric pressure.
The pressure of the gas will be
measure in comparison with the
atmospheric pressure.
If the difference in height, h is due to
the gas pushing the mercury more
than the atmospheric pressure pushes
the mercury, then the gas pressure is
in excess of the atmospheric pressure
by h cmHg.
Implying gas pressure = (76cm + h )
cmHg
But if the atmospheric pressure
pushes more by a difference in
hcmHg, then
The gas pressure = (76-h) cmHg