Chapter 1 part 6 : Work, Energy & Power

                                            General Physics  

• 1.95: Energy & Resources.

Energy is present all around us in many many forms, Energy cannot be created or destroyed
Only changed from form to form, Such as from kinetic energy to thermal energy or from chemical energy to electrical energy. these changes occur  due to events such a burning fuel or moving an object to a higher location or the flow of a current from a battery.
An even such as the moving of a car involves the energy change from chemical energy in fuel to thermal energy once ignited , this then converts to kinetic energy as the car thrust forward and back to thermal due to frictional forces. All of the chemical energy initially in the fuel has changed into thermal energy and kinetic energy , No energy is destroyed in the process.

Not all energy is useful to us ,such as the thermal energy lost as friction or the chemical energy present in fossil fuels , we change the type of energy in order for it to be useful , For example , in water falls the fast moving water has alot of potential energy , this is then used to drive a turbine which in turn drives a motor to produce electrical energy which is useful to us as we use electrical energy to drive our electronics and household appliances
forms of energy transfer we use are: solar energy, wind energy , nuclear energy , geothermal energy and tidal energy.
Some forms of energy transfer are more efficient than others, for example solar energy is very inefficient  as most of the energy radiated from the sun is not transferred , while nuclear fission produces large amounts of energy from small samples of radioactive material such as uranium or plutonium. Although efficiency may be a problem , some energy sources are non renewable , meaning that they cannot be harvested forever , wind and solar energy are continuous and do not run out and can be considered to be renewable whilst fossil fuels such as coal and natural gas and oil are finite and can run out.

Efficiency can be calculated as useful energy output/ total energy input *100

• 1.97: Work & Power

The work done in any scenario is the energy transferred , this can be written mathematically as W=F.S which is Work equals Force.Distance which is equal to energy change .  So the work done is equal to the force moved in the direction of the force causing the motion.
Power is the term we use to describe the rate of doing work , How quickly a motor can burn through fuel can be described through its power, And is equal to Work/Time.

• 1.99: Pressure

Pressure is equal to Force/Area for a single force against a surface, In a liquid pressure is equal to the density of the liquid.Acceleration due to gravity.the height of the liquid
A device known as a barometer is used to measure atmospheric pressure, the device contains mercury , at sea level the barometer read 760 millimeters of mercury , at higher altitudes the pressure decreases due to there being less air above you creating that pressure.
A device used to measure pressures in general is a manometer , which works in the same way as a barometer but using a tube to input a liquid or gas into the apparatus instead of using the atmosphere.

Chapter 1 part 5: Vectors & Momentum

                                       General Physics

• 1.8: Scalar & Vector ; centers of mass

In physics we describe certain quantities such as distance , time , weight, mass, Electric current, volume etc. We can class every kind of value into two groups, Scalar and Vector.
Every quantity has magnitude, but not all quantities have a direction.

E,G. A length of rope is described to be 10 Meters long. The magnitude of its length is 10 meters, this value has no direction as it is 10 meters long no matter what. and is therefore a scalar quantity 
But if i am measuring displacement, a vector quantity, No matter how much distance is actually traveled, the displacement is the distance from the end point to the start point, For example , a car moves 10 meters north then 10 meters West Then 10 Meters South. The car has moved 30 Meters distance wise , but has a displacement of 10 meters west of its starting point.
Vectors has magnitude and direction while scalars only have magnitude.

Every object has a center of mass , This is a point where all the weight of an object can be considered to act, if an object is tilted over its own center of mass , it will topple and fall. stable objects have very low centers of mass.
A sphere will have a center of mass right in the middle of the sphere while an upright rectangle will have one halfway up the length of the rectangle. this is why a rectangle will easily fall if you push it while a sphere will roll, since the center of mass is always in the same spot , the sphere is in equilibrium and does not move if left alone. A very unstable object may topple on its own within seconds if left alone

• 1.9: Momentum 

Any object that moves has momentum , momentum is equal to Mass.Velocity , if a moving object has a large momentum , a large force is required to stop it, Inertia is an objects tendency to stay still , so objects of high momentum have low inertia. The equation for momentum is P=M.V, where p is momentum , M is mass and V is velocity

Another quantity known as impulse is the change in momentum. A force is equal to the rate of change of momentum , so the change of momentum is newtons second law for force multiplied by time , so Impulse is equal to Force.Time

Momentum is always conserved, if an object  that is moving at a certain speed collides with another object , then the second object will start moving , gaining the momentum lost by the Initial object.
For example , if a car crashes into a garbage can that is stationary , if the car has a momentum of 500 newton meters , and the car comes to a stop at the garbage can , then the can will gain 500 newton meters of momentum, moving very quickly due to a much smaller mass.
mathematically this is shown in the equation (M1U1 + M2U2 = M1V1 +M2V2) where U is initial speed and V is final speed.

Chapter 1 part 4: Forces & Moments

                                         General Physics

 

• 1.5: Forces & Springs 

Forces act all around us all the time , these forces may be due to the weight of an object , the thrust of an engine or the pulling of a lever. A force is a push or pull and can be calculated as Force equals Mass.Acceleration , F=M.A. Forces applied to objects can cause them to change shape, to deform.
When an object deforms due to a force , it can either extend or compress , get longer or shorter.
Take a spring for example , the amount a string stretches is proportional to how much force we put into stretching it , This can be written as F∝X where X means extension. Every spring made of different materials stretches differently , and has a vale known as a spring constant. Hence exists Hooke's Law , F=K.X where K is the spring constant  

Metals tend to extend uniformly , meaning the above equation applies very well to metals. this means that when we plot a graph of force/extension , we get a straight line , until the metal is close to reaching its breaking point , it is proportional , a metal will not stretch proportionally near its breaking point as shown in the diagram.

• 1.6: Forces & Motion

In motion, forces cause objects to accelerate , since F=M.A , But rarely is there a case where only one force acts on a body , There are usually several forces acting , but how do we deal with all of these forces ? , The answer is that forces acting in the same direction can be considered to act as one force , and you can add their magnitudes together, So if a car is moving along a road with a thrust of 5000 newtons and is at the same time experiencing friction with the road , of magnitude 1000 newtons , since these forces are considered to act in opposite direction , the resultant force is 4000 Newtons in the forward direction.

If there is no resultant ,that means that all forces are balanced in all directions, then there is no acceleration , so no change in velocity , this means that a body with no resultant force actin will move at constant speed or stay at rest (since rest is a constant 0 speed).

Friction such as that in the diagram is due to the roughness of the road and resists the motion of the car , there is also air resistance, as the car moves it is moving through the air as well , which blocks the motion of the car . Submarines experience water resistance, since water is much denser than air it resists the motion of objects within it much more than air does.

The types of resistance you need to know are : Air resistance, Water resistance and Drag (general term for resistance)

• 1.7: Moments & Turning effects

The moment of a force is the magnitude of its turning effect. This means that if a force acts about a pivot , causing an object to turn about that pivot , then this force has created a moment about the pivot.

E.G.
If i am pushing open a door that swings sideways , i am creating a moment about the door hinges. If i push hard against the door it will turn faster as i will have created a larger moment. if i push further away from the pivot the door also becomes easier to push , as this too creates a larger moment
This is due to the fact that a Moment equals Force.Perpendicular Distance from the pivot.
So by increasing the magnitude of the force or the distance from the pivot , we can create a larger turning effect.

The principle of moments
This is a rule that if the moments about a pivot are balanced , This means moment in the clockwise direction are equal in magnitude to moments in the anticlockwise direction, the object can then be in equilibrium 

For an object to be in equilibrium : Sum of clockwise moments are equal to the sum of Anticlockwise moments. And that no resultant force acts upon the object . If these two conditions are satisfied then the object is in equilibrium
                                                   

Chapter 1 part 3: Mass, Weight and Density

                                            General Physics

• 1.3: Mass and Weight.

All objects composed of matter have mass, anything comprised of atoms can have mass. Weight is just the effect of gravity on a mass. So if a 1 kilogram iron bar is weighed on earth compared to in outer space , the weights will be different ( due to different gravitational fields) while the Mass will be exactly the same.

E.G.
A car weighs 4900 newtons on earth and has a mass of 500 kg . In a zero-gravity environment the car will still be 500 Kilograms but weight 0 newtons. this is because weight is a gravitational force that requires a gravitational field, like on Earth !

So Force is equal to Mass . Acceleration , F=M.A. Since weight it a gravitational force it can be calculated using the same equation , with the acceleration due to gravity being 9.8 or 9.81 , (sometimes 10 for simplicity) , We simplify this into Weight is equal to Mass . Gravity , W=M.G

• 1.4: Density

So mass is the amount of matter in an object in total , density describes how closely packed that matter is together on average. Density is equal to Mass/Volume. as the equation tells us , it is the amount of mass there is per cubic meter or centimeter. To put this into comparison We will ask a question

Q&A:
Q: Which is heavier , 1 kilogram of feathers or 1 kilogram of steel ?
A: the answer is , they have the exact same weight ! , but due to different densities , you need a large volume of feathers to make 1 kilogram , while you only need a small sample of steel in order to make 1 kilogram

So how do we measure densities ? , well we consider the density of water to be 1000 kilograms per meter cubed. if we know the mass of an object but not the volume , we can perform a simple experiment, we simply submerse the object in a known volume of water in a graduated flask or measuring cylinder. we take note of the initial volume (before adding the object) and the final volume ( after adding the object) the difference will equal the volume of the object and the density can be found by dividing mass by the volume found.
If an object is less dense than water , it will float when put into water . That is why oil stays on the surface of water and do not mix. for the same reason a rock sinks in water as it is more dense.

Chapter 1 part 2: Motion

                                         General Physics

• 1.2: Motion

    When we want to describe the motion of an object , we can talk about how fast it is going, its         speed, and what direction it is going. the speed of an object is how much distance it moves per unit of time , Speed=distance/time.. While in physics we also use the term velocity. Velocity is displacement/time . unlike distance, displacement is the smallest distance between the end of an objects journey and its beginning.

E.G

If a car on a race track completes one lap around the track , and the track is 500 meters long, the car will have a distance traveled of 500 meters , but a displacement of 0 , since the car will have returned to its starting point.

Motion graphs:

We can plot certain quantities about the motion of an object against time
these quantities being 

• Distance
• velocity
• acceleration

Acceleration is the rate of change of velocity. we can calculate acceleration from a velocity time graph by finding the gradient of the line at any one point. Since the equation for gradient is actually the change in Y/ the change in X , actually being the change in velocity over a period of time.
We can also find distance traveled by an object through a velocity time graph. The area under the line in a velocity time graph is equal to distance traveled by the object

Chapter 1 part 1: Length and Time

                                            General Physics

•  1.1: Length and time.
  
  For the beginning of your IGCSE Physics course you will need to be familiar with the idea of measurement.

We can measure distance in the SI base unit Meters (M) and time in the SI base unit Seconds (S)
You will need to know some rules about measurement. We can measure using two kinds of apparatus
Digital and Analogue 


A digital display shows one value at a time , while an analogue display , such as in a car speedometer, shows a range of values


For very small increments of time in the case of fast moving objects, we can take an average over many experiments.
E.G. If a pendulum swings quickly from side to side , in order to find the time for one oscillation. you will time how long it takes for 10 swings, and divide that number by 10
To measure time we can use a clock or stopwatch.To measure distance we can use meter rules or tape measures for lengths, and use micrometer screw gauges and vernier calipers for thicknesses

Q&A:

Q:How to measure the length of a string without a ruler ?
A:First, we can wrap the string around a cylinder as many times as possible for the full length of the string. for example , if the string goes 3 times around the cylinder , and the cylinder has a diameter of 3 cm , then the string is 9 cm long.