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