EDEXCEL PHYSICS NOTES FOR UNIT 1 has been attached:
If there are any doubts, do comment and ask them out.
Notes are about Motion & forces:
Physics notes for motion and forces.
Physics unit 1 notes excerpt: available for download.
SPEED:
Average speed of an object can be
defined by the following equation:
average speed (m/s) = distance covered in
metres(m); time taken to cover distance in seconds(s).
Speed and velocity:
The speed is defined above, Whereas, the word velocity,
is defined as speed in a particular direction – for example a bus has a
velocity of 30 m/s in a forward direction.
Definition: velocity is
a speed in a particular direction.
Distance–time graphs:
When an object moves along a straight line, we can represent how
far it has moved using a distance–time graph. Graph below: is a
distance–time graph for a runner. She sets off slowly and travels twenty m in
the first ten seconds. She then speeds up and travels the next twenty m in five
seconds.
Speed can
be calculated using the gradient of the graph. Steeper gradient increasing
with time tells that her speed is
increasing. We can calculate the speed at any point by drawing a tangent to the
curve, and then measuring the gradient.
Investigating motion
The aim of this experiment is to determine the speed of an object
or a person, by measuring how long it takes something (or someone) to cover a
measured distance.
Acceleration:
When a car is
speeding up, we say it is accelerating. It is deceleration, when it is slowing
down.
A car that
accelerates reaches a maximum speed in a short time. For example, a bike might
speed up to 12.5 m/s in 5 seconds. A bus could take longer time , 10 s, to
reach the same speed. So the acceleration of the bike is twice as big as the bus’s
acceleration.
You can calculate the
acceleration of an object using the equation: 
where acceleration, a, is in
metres per second squared, m/s2
change in velocity (v
− u) is in metres per second, m/s v is the final velocity
after something has accelerated and u is the velocity before the
acceleration.
time, t, taken
is in seconds, s
TIP
The units of acceleration are m/s2.
Velocity–time graphs:
In section A; It has a Positive
Gradient means the velocity is increasing and so it is positively accelerating
B- There is no gradient as the
car is moving at constant velocity and there is no acceleration.
C-There is a negative gradient
indicating a decrease in velocity and a decrease in acceleration (decelerating)
D-There is no movement of the
car as car has come to stop hence the gradient , velocity and acceleration are
all 0(v = 0) (a=0) (g=0)
The gradient of the graph gives us the
acceleration. You can also work out the distance travelled by calculating the
area under the velocity–time graph.
Observing and calculating motion
The speed of a moving object can also be
measured using light gates.In experiment to determine the acceleration of a
rolling ball as it passes between two light gates. When the ball passes through
a light gate, it cuts a beam of light. This allows the computer to measure the
time taken by the ball to pass through the gate. By knowing the diameter of the
ball, the speed of the ball at each gate can be calculated. You can tell if the
ball is accelerating if it speeds up between light gates A and B. 
Equation of
Motion
When an object accelerates in a straight line, the final speed,
initial speed, the acceleration and the distance travelled may be connected by
the following equation.
v is the final velocity in metres per
second, m/s
u is the initial (starting) velocity in metres per second, m/s
a is the acceleration in metres per second squared, m/s2
s is the
distance in metres, m.
Introducing forces
What is a
force?
A force is a push or
a pull. The forces that you exert can cause three things:
·
You can change the shape of an object. You can stretch or
squash a spring. You can bend or break a ruler.
·
You can change the speed of an object. You can increase the speed of a ball when you throw it. You decrease its
speed when you catch it.
·
A force can also change the direction
in which something is travelling.
The
forces described so far are called contact forces. Your hand touches
something to exert a force.
There
are also non-contact forces. Gravitational, magnetic and electric forces
are non-contact forces. These forces can act over
large
distances without two objects touching.
The unit we use to measure force is the newton
(N). Large forces can be measured in kilonewtons, kN.
Vectors and
scalars:
Vector quantities have both size and direction.
Scalar quantities only have size.
Speed is a scalar because we only define how fast
something is moving. Some examples of scalar quantities are: mass (3 kg of
potatoes); temperature (20 °C); energy (100 joules).
Velocity. is a vector quantity because we should
define both a size and a direction. Other examples of vectors are: velocity
(the wind blows at 50 km/h, from the North); displacement (a car travels 20 km
due East).
Some
important forces:
Weight:is the name
that we give to the pull of gravity on an object. Near the Earth’s surface the
pull of gravity is approximately 10 N on each kilogram.
Tension: is the name
given to a force that acts through a stretched rope; when two teams pull on a
rope it is under tension.
Friction: is the
contact force that slows down moving things. Friction can also prevent
stationary things from starting to move when other forces act on them.
Drawing
forces:
It is usual for more
than one force to act on object. Then we must show all the forces acting. When boy
is pulled by the rope (Figure 4.5), his weight still acts on him, and the floor
supports him too – if the floor did not exert an upwards force on him equal to
his weight, he would be falling downwards. The force is called the floor’s
normal contact force, R. The floor will also exert a frictional force on him,
in the opposite direction to that in which he is moving.
All these forces are
shown together in: 
Adding forces:
When two forces act in the same direction, they add up to give a
larger resultant force. If forces act in opposite directions they may cancel each other
out. The resultant force is zero. We say that these forces are
balanced. The pull from the rope to the right is 150 N, but the frictional
force to the left is 50 N. The resultant horizontal force on boy is therefore
150 N − 50 N = 100 N, to the right.
Newton’s first law: balanced forces:
When the resultant force acting on an object is zero, the forces
are balanced and the object does not accelerate. It remains stationary, or
continues to move in a straight line at a constant speed.
The speed and/or direction of an object will only change if a
resultant force acts on the object.
Newton’s second law: unbalanced forces:
When an unbalanced force acts on an object it accelerates. The
object could speed up, slow down or change direction. Newton’s second law
states that
• acceleration is proportional to the resultant force: 
• acceleration is inversely proportional to the mass: 
This
can be written as an equation:
resultant force = mass × acceleration where force is in newtons, N
mass is in kilograms, kg acceleration is in metres per second
squared, m/s.
Very good and useful information
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