Forces, Transport and Communication

Newtons Laws of Motion:

1st Law- An object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

2nd Law- F=ma

3rd Law- Every action has an equal but opposite reaction

An Object only changes velocity when there are unbalanced forces acting on it

A force has two Components:

1. Magnitude
2. Direction

We can add forces together. The sum of the forces is called the resultant force. 

What is the resultant force on this 1000kg car?

500N - 200N = 300N 

Using Newton's second law (F=ma), calculate the cars change in velocity

Displacement is…

• how far an object has travelled from its starting point
• Area under the curve in velocity time graphs

Time point (seconds)

Velocity (m.s -1)

0-5

1

5-10

1

10-15

0

15-20

-3

20-25

1

Changes to the gradient of velocity-time graphs show acceleration

Internal Combustion Engines

How does a modern car engine work?

1. Intake - the piston is pulled down inside the cylinder by the momentum of the crankshaft. Most of the time the car is moving along, so the crankshaft is always turning. The inlet valve opens, letting a mixture of fuel and air into the cylinder through purple pipe.
2. Compression- The inlet valve closes. The piston moves back up the cylinder and compresses the fuel-air mixture, which makes it much more flammable. When the piston reaches the top of the cylinder, the sparking plug fires
3. Power- The spark ignites the fuel-air mixture causing a mini explosion. The fuel burns immediately, giving off hot gas that pushes the piston back down. The energy released by the fuel is now powering the crankshaft.
4. Exhaust- The outlet valve opens. As the crankshaft continues to turn, the piston is forced back up the cylinder for a second time. It forces the exhaust gases (produced when the fuel burned) out through the exhaust outlet. 

Oil based fuels are used in the internal combustion engine. A controlled explosion is used to drive a piston up and down in a cylinder. (1.2) 

Energy transfer diagram for a car:

Chemical Energy, Heat Energy, Kinetic Energy (movement)

Wasted Energy:

• Sound
• Heat
• Light

In 1885 Karl Ben invented the car by taking an internal combustion petrol engine designed by Nikolaus Otto and attaching it to a 3-wheeled cart

Frank Whittle was the first inventor of the Jet Engine. 

How a jet engine works

Jet engines work on the same principle as the internal combustions engine. 

1. Air drawn in at the front and mixed with fuel
2. Fuel and air mixture compressed by a fan
3. Fuel and air mixture combusted
4. Exhaust is forced out at rear of engine 

Each main part of the engine does a different thing to the air or fuel mixture passing through:

• Compressor: Dramatically increases the pressure of the air (and, to a lesser extent) its temperature.
• Combustion chamber: Dramatically increases the temperature of the air-fuel mixture by releasing heat energy from the fuel.
• Exhaust nozzle: Dramatically increases the velocity of the exhaust gases, so powering the plane.

Jet Engines are subject to very large tensile forces and special materials have been developed to cope with these (1.2, 1.10) 

Jet Engines are 'better' than internal combustion engines because:

1. The fuel to air ratio is greater (1:50) which allows more fuel to be combusted over longer periods
2. Because intake, compression, combustion and exhaust all happen simultaneously, there is more power per time unit
3. Minimum of moving parts, therefore less energy is lost through the 'mechanics' of the engine.

Electric cars use stored electric energy to produce motion. Some modern cars have a hybrid petrol-electric engine. Both these technologies require a battery of cells to be carried in the vehicle. (1.2)

Hydrogen- cell transport: hydrogen gas is used in a fuel cell to produce electric current with water as its waste product (1.2)

Hydrogen Fuel Cells:

• Device converts hydrogen into energy using water
• One bi product which is water
• Produce hydrogen and then use it to produce energy
• Research is done to reduce the use of expensive metals
• Demand and leading new technology

Petrol

Electric

Pro's

Con's

Radio waves are reflected by charged particles in a part of the atmosphere called the ionosphere 

AM Radio (Amplitude Modulation)

• The Amplitude (height or volume) of the high frequency carrier wave is used to match the shape of the audio wave
• AM radio signals have frequencies between approximately 500-1000 kHz

FM (Frequency Modulation)

• In FM radio the frequency of the carrier wave is adjusted to hold the shape of the sound wave
• FM radio has frequencies of about 100 MHz and human ears can hear up to 20 kHz

James Clerk Maxwell was able to unite the theories of Electricity and Magnetism. His formulae predicted a whole range of waves with the same speed as light.

Visible light:

• The frequency and wavelength range
  • Wavelengths in the range of 400-700 nanometres
  • Between infrared and ultraviolet
  • Frequency of 430-750 THz (terahertz)
• Uses
  • Used by the optic organs of humans and animals
  • It is used to help us see - for example the reflection of the sunlight off objects around us

• Dangers or risks
  • Too much light can cause damage to the retina cells, which increases the risk of developing age-related macular degeneration (eye condition in which the portion of the retina involved with sharp, central vision deteriorates)
  • It can also do damage to the skin 
  • If a person doesn't close their eyes right away prior to exposure to very bright light, this can cause temporary blindness

• Any links to communication
  • Fibre Optics
  • TV
  • Film

Analogue and Digital Signals:

• Communication signals may be analogue or digital
• Analogue signals vary continuously in amplitude between zero and some maximum level
• Digital signals only have two voltage levels, for example +5V and 0V. These values are called 0 and 1 (or ON and OFF)

Modern Digital Signals:

Spec Point- The electronic circuit involved operate according to Boolean logic using electronic gates (1.6, 1.12)

The use of digital conversion has only become possible in recent decades because of the increased speed of computers carrying out analogue to digital conversion.  

Logic Gate:

• A component within a complex circuit
• A gate is a simple circuit that decides what to do with an input signal (either on or off)

Example

• AND gate (used for multiplication)

 What is a binary number?

• A number that consists of typically 0 and 1 

Spec Point: A wave may be converted to a digital signal by successively sampling the amplitude of the wave and the process reversed to recreate the wave 

Advantages of digital signals:

• Less affected by interference
• Interference is not increased when the signal is amplified
• Uses weaker signals than analogue

Key Term

Definition

Diffraction

the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the wave forms produced.

Reflection

When light bounces off an object

Refraction

change in direction of a wave passing from one medium to another or from a gradual change in the medium.

Angle of incidence

In geometric optics, the angle of incidence is the angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal.