Other physic Book Note On Things Learnt Or Not

Motion: 

the modern study of motion is divisible into two distinct parts:

kinematics and dynamics.

kinematics is the study of motion without regard to its causes. dynamics investigates the causes of motion, that is, it looks at forces. 

Describing motion:

terms used when describing motion are: distance, speed, velocity and acceleration.

the simplest motion is linear or rectilinear motion, that is, motion in a straight line. the simplest of these is motion with constant speed and the next simplest is motion with constant acceleration. complex motions include circular motion and projectile motion.

Motion occurs when an object changes its position relative to other objects or some coordinate system.

Quantitative description of motion:

science is quantitative, that is, it relies heavily on measurement for its description. for motion, the most important quantitative description is the speed of an object.

SPEED

the speed of the object is the rate at which the object changes its position.

speed is the time rate of change of distance.

there are two types of speed, average and instantaneous.

Average speed:

the average speed of an object is defined as: average speed = distance / time

units: the common everyday unit of speed is kilometres per hour, whereas the scientific unit, is metre per second. it follows that. 

1 km / h = 1000 m / 3600 (hour to seconds).

instantaneous speed:

speed at any particular instant is called instantaneous speed.

v = triangle s / triangle t

where the triangle, delta, means a change in. the instantaneous speed is equal to the change in distance divided by the corresponding small change in time. 

constant speed:

an object such as a car is moving with constant speed when it travels equal distances in equal intervals of time. in the special case of motion with constant speed with constant speed, the average speed and the instantaneous speed are numerically the same, that is, they have the same value. 

Speedometer:

a cars speedometer measures the speed of a car at each instant, that is, it measures the instantaneous speed (to a good approximation).

Measuring speed:

to calculate speed of an object we need to measure distance and time.

to measure distance and time to calculate speed might use the following:

a ruler and stop watch.

a tickertimer.

electronic and/or computer timing.

a blinky/strobe utilising multiflash photography.

Ruler and Stopwatch

these two devices re useful when we are dealing with relatively long time intervals (anything more than a few seconds). for example, we might use them to determine the average velocity of a runner at a school sports carnival bytes method. it would however, be difficult to use this method to measure the runners, instantaneous speed. this is where the following methods can be used:

ticker timer: 

this device consists of a magnet and a hammer arrangement that results in the hammer marking paper ticker tape at regular time intervals as the object pulls the paper through the timer. the timers generally operate at the electricity mains frequency of 50 Hx, that is the hammer strikes the paper 50 times per second, leaving a mark on it. it follows that the time interval between strikes is 1/50th of a second. 

the distance between successive dots indicate the speed of the tape and hence the object to which it is attached. the closer the dots, the slower the object was moving, the further the dots are apart the faster the object,

Momentum

a truck requires a large force to set it in motion when it has a full load than when it is empty. likewise, far more powerful brakes are needed to stop a train then a pushbike moving with the same velocity. when two bodies, a heavy one and a light one, are acted upon by the same force for the same tiem, the light body builds up a greater velocity than the heavy one. the heavy vehicle is said to have a greater amount of momentum than the lighter one.
if we take newtons second law f - ma and replace the acceleration with its definition as the time rate of change in velocity, a = v / t.
f = mv / t
the force is now defined as the change in mv with time.
the produce of mass and velocity is called momentum and we give it the symbol p.
momentum = mass x velocity.
p = m v
where p = momentum measured in kg m s -1
m = mass measured in kg
v = velocity measured in ms to negative 1 square.
if we assume that f is zero, then the change in momentum p must also be zero. thus if there are no external forces acting on an object, the momentum of the object is constant.
momentum is a vector measurement. it is an indication of how hard it will be to stop an object.
the momentum of any object will never change if left alone.

Friction & The Difference Between Mass and Weight

The Difference Between Mass and Weight:
mass is the quantity of matter that makes up an object. it is measured in kilograms.
the weight of a body is the force it normally exerts on anything which supports it. a body exerts this force owing to the fact that it is itself attracted towards the earth by the force of gravity.
weight = mass x acceleration due to gravity
f     = mg
  w
a 1 kg object on earth weighs 1 x 9.8 = 9.8 N. the same object on the moon, where the acceleration due to gravity is 1 / 6 that of the earth, weights 1 x 9.8 / 6 = 1.63 N. the object has the same mass in both places, but the weight is different, due to the differences of the gravitational pull of the two planets.

Friction:
friction is a contact force that opposes motion. friction slows a moving object down. friction is also the force that stops stationary objects from moving. it plays an important role in our daily loves. walking would be impossible if there were no friction between the ground and the soles of our shoes. without friction, brakes would not work.
friction can be a nuisance, because when two surfaces rub together they convert kinetic energy into heat energy. when an object becomes hot, it expands and takes up more space. the inside of a car engine becomes very hot. it is necessary to reduce the heat generated, and consequently reduce the expansion of the engine components. we add oil to an engine to do this. a layer of oil between two surfaces acts as a cushion, reducing the friction between two surfaces rubbing together. air resistance is another example of friction. the greater the velocity of an object moving through the air, the greater the amount of air being pushed out of the way by the object. air resistance depends on the shape and the speed of the object. a truck with a large surface exposed to the air has to move a greater amount of air, therefore a greater force us needed to move at it at the same speed as a smaller object, such as a car. modern cars are designed to cut through the air with the least resistance, therefore they have small surfaces exposed to the air.

Newton's Law's Of Motion

Newton's First Law of Motion: the Law of Inertia
An object will continue in a state of rest, or uniform motion in a straight line at constant velocity, unless an unbalanced external force causes it to change the state.
inertia is a property of any object. it involves both the amount of motion (velocity) and the mass content ( mass of an object).
the law of inertia is simply the statement that any object resists any change in its state of motion or state of rest if not moving.
the degree of resistance an object offers to a change in motion is directly proportional to the mass of the object. it is much easier to move a 1 kg mass than it is to move a 100 kg mass. this is because 100 kg has more inertia. to move each vehicle, you have to overcome its inertia. because the 'motorcycle' has less mass it has less inertia.

Newton's Second Law Of Motion:
an unbalanced external force will change an objects state of motion by producing an acceleration. the force is equal to the product of the mass and acceleration of the object.
force (net) = mass x acceleration.
f net = ma
m = mass in kilograms (kg)
a = acceleration in metres per second
fnet = net (unbalanced) fore, which produces the acceleration in newtons.


Newtons Third Law of Motion:
for every action (force) of an object, there is an equal and opposite reaction by the object upon the agent (for every action done by an object, the object that had just been placed with this action will exert an equal and opposite reaction back open the object). when you walk, your foot pushes on the ground while the ground pushes upward on your foot, the two forces being equal and opposite.
forces always come in pairs. important points to remember in relation to netwon's third law are that the two forces, the action and reaction force, are both equal and opposite, and they are acting on different objects.

Force & Relative Motion

Relative Motion:
The motion of two or more objects can be viewed in different ways the motion can be compared to a stationary object, e.g. the ground, or it can be compared to another moving object.

Force: 
A force is simply a push or a pull on an object. When you push any object you are exerting a force on it. Forces surround us all the time. However it is not possible to describe a force as we can describe some object.
We can only describe what a force can do.
When a net force acts on an object it can:
-change the velocity of the object, either accelerating or decelerating it.
-change the direction that the object is moving in
-change the objects shape, or deform it. 


Contact forces: 
Contact forces are forces that act in contact with the object. Contact forces operate when particles or objects are in direct contact with each other i.e: when a wheel of any object is in contact with a road surface, when a person sits on a seat, when the wind blows against you.

Non-contact forces: 
Non contact forces are forces that can act on an object over a distance. i.e: gravitational, electrical, magnetic, and nuclear.
Gravitational force pulls us down even if we are not in contact with the earth, stops the loss of small particles from earth to space and influences the earth and other planets revolving around the sun.
Electrical force is the force between charged objects. Thunderstorms are a spectacular display of electrical forces at work.
Magnetic force which is related to electrical force, is responsible for the repulsion of two like magnetic poles when they are brought close together.
Nuclear forces are the forces acting between the many particles that make up the nucleus of an atom.


Spring Balance:
A spring balance is a common piece of equipment used to measure force in a laboratory.
This is how it works:
When a force is applied to the balance, a spring extends. This spring is attached to a pointer which indicates the force on a calibrated scale. The greater the force, the greater the extension of the spring. Force is measured in newtons. This unit of force is named after Sir Isaac Newton, a famous british scientist. A force of one newton will accelerate a mass of 1 kg at a rate of 1 m s to the power of negative 2.

DISCLAIMER: I DO NOT OWN THESE NOTES ALL RIGHTS BELONG TO THEIR OWNER: THE AUTHOR OF MY WORKSHEETS, THE AUTHOR OF MY BROUGHT, GIVEN OR BORROWED TEXTBOOKS. 

AND LASTLY, THE WORKS GIVEN FROM MY SCIENCE TEACHER. 

Quantities in Physics

Measurement:
Motion is the change in the position of a body (i.e a car) with respect to time. We have a standard of measurement so that they way of describing the change in position means the same thing to everyone.

Standard of Measures:
Nearly all quantities in the physical world, can be expressed in terms of four fundamental quantities.
The four fundamental quantities are those of length, time, mass, and electric current. All other quantities are called derived quantities, because their measurement involves the measurement of two or more of the fundamental quantities.
The standards we will use in this unit are length, time and mass.
A standard must be unchanging, accessible, and reproducible.
The relationship between a derived quantity and the fundamental quantities can be made clear by the use of dimensions. When using dimensions we represent length by L, mass by M and time by T.

Dimensions of Some Common Quantities:
Quantity: Area, Relationship: length x breadth, dimensions: L square (in number form)
Quantity: Velocity, Relationship: displacement over time, dimensions: L T to the power of minus 1.
Quantity: Acceleration, Relationship: velocity over time (meaning that we need to find the velocity of an object before finding the acceleration of it, that is, if you want to find it), dimensions: LT over the power of LT-2.
Quantity: Force, relationship: mass X acceleration, dimensions: M L T to the power of negative 2
Quantity: Momentum, relationship: mass X velocity, dimensions: M L T to the power of negative 1.
Quantity: Work, relationship: force X distance, dimensions M L square T to the power of negative minus one.

Scalar and Vector Quantities:
A scalar quantity has magnitude but no direction. Distance is an example of a scalar quantity. It is measured in meters but has no direction.
A vector quantity has magnitude and also direction. The vector quantity displacement is the measure of the distance between where an object started and where it finished for example, 100 m and since vector quantities includes direction also, 100 N.
A vector may be represented by a line with an arrowhead, where the 'scaled' length of the line represents the magnitude of the vector and the arrowhead shows the direction.
i.e: vectors will look like this...

---------------------->
   20km east.

Change in velocity = final velocity - initial (starting) velocity

Speed and Velocity: 


Speed:
average speed = distance/time taken
                      s = d/t

The term average speed is called that because even when an object is travelling on a straight road, there are minor changes in the objects speed due to the surface of the road as it might be bumpy etc.
Speed is usually measured in meters per second, m s over the power of one or m/s.

The formula again:
speed   = d/t
       av 
We need to distinguish between average and instantaneous speed.
The instantaneous speed of an object is the speed of the object at any given moment.

Velocity:
Velocity is a vector quantity, it has magnitude and direction.
Velocity is defined as the time rate of change in displacement (displacement meaning the magnitude and direction--so, the time rate of the change in direction and magnitude of an object i.e: a travelling car). This simply means that average velocity is the displacement divided by the time taken.

Average velocity = displacement / time taken.

In dimensions:
v    = s /t
 av
v   = average velocity, measured in meters per second.
 av
s = displacement, measured in meters
t = time, measured in seconds

When acceleration is constant:
average velocity = final velocity + initial velocity / 2

v    = v + u / 2
 av 

Acceleration:
Acceleration is the time rate of change in velocity. This means that we can find the acceleration of an object by dividing the change in its velocity by the change in time.

Acceleration = change in velocity / change in time.

a = v / t
a = v - u (final velocity - initial velocity) / t
This equation can also be written in the form: v = u + at


When calculation if the calculation has a negative sign in front of the answer it means that the person or object is slowing down, or decelerating.

Displacement:
Displacement is the distance moved by an object in a specified direction. Displacement is a vector quantity (it has both magnitude and direction).


The equation for displacement is:
s = ut + 1/2 at the the power of 2 (square)


                     2
s = ut + 1/2at


Where:
s = displacement measured in meters (m)
u = initial (starting) velocity measured in meters per second.
a = acceleration.
t = time measured in seconds (s)

DISCLAIMER: I DO NOT OWN THESE NOTES ALL RIGHTS BELONG TO THEIR OWNER: THE AUTHOR OF MY WORKSHEETS, THE AUTHOR OF MY BROUGHT, GIVEN OR BORROWED TEXTBOOKS.
AND LASTLY, THE WORKS GIVEN FROM MY SCIENCE TEACHER. 

Speed/Time Graphs

Like distance and time speed and time can be placed visually on a graph as well. The steeper the slope, the faster it is either accelerating or decelerating.
Acceleration is the change in speed over time.
Usually in a speed time graph, the equation of the slope is still the y axis over the x axis in which y represents the speed, and x represents the time.
The area under the line represents the total distance. Using mathematical formulas you can find the area under the line.
Once the slopes are divided into geometric shapes either usually, triangles or squares you can find the distance, you must know these formulas however.
Triangle: b x h / s
Square: b x h

Note: notice that distance, time, speed are all related to each other.


DISCLAIMER: I DO NOT OWN ANYTHING, ALL INFORMATION AND RIGHTS BELONGS TO http://library.thinkquest.org/C0110840/speed-time.htm 

Distance/Time Graphs

Distance time graphs is a visual way to show a collection of data. It can help understand the relationship between the data.
In a distance time graph, the x axis is the independent variable (component you can change--in other words it is not fixed) and shows time in seconds. On the y axis, it shows distance in meters, and it is the dependent variable (component you cannot change--in other words, it is fixed).
If the points on a line graph do not form a straight line, a line of best fit must be drawn in.


TO FIND THE SLOPE (SPEED) OF A LINE:

The slope of a line determines the speed. The higher the slope the greater the speed but if the slope is low, the speed is also low.

In other words, if the slope is high, then the speed is great. If the slope is low, the speed is low. 

Equation for a line: y = mx + b
m is the slope of the line,
b is the y intercept of the line
y is the dependent variable, on the y axis (distance).
x is the independent variable, on the x axis (time).


In a distance/time graph the equation changes from 


y = mx + b to d = v / t


d is the dependent variable (distance)
t is the independent variable (time)
v (speed) is the slope of the line.

We can find the slope of a line by using maths which says to find the slope, we have to divide rise over run.
To find the slope using the v = d/t formula we do this,
d (the slope (speed)) is = to the change in distance (on the y axis) / the change in time (on the x axis).
basically:
slope = rise/run or v = d/t

The slope of a line is calculated as follows:
For example...
d = d1 - d2      (because we are calculating the change in distance, and from d1 - d2, we calculate the change in distance by subtracting--which we need change in distance for the equation.)
  = (insert number here) meters
t = t1 - t2         (remember, we are finding out the change of the time this time, so we can divide it with the distance to get the slope to find the speed).
 = (insert number here) seconds
Then finally, get both calculations and put it into the equation:
v = d / t
It will equal v = (insert number here) m/s (meters over seconds)

Note: it does not have to be in m/s if a graph says in the dependent axis kilometers and on the independent axis minutes the result of the slope will be v=(insert number here)km/min.

DISCLAIMER: I DO NOT OWN ANY OF THIS INFORMATION ALL INFORMATION AND ALL RIGHTS BELONG TO http://library.thinkquest.org/C0110840/speed-time.htm