MOTIONThe Four-stroke Petrol EngineVehicles without Engines1. Many vehicles do not use engines to move about e.g. bicycles,bullock carts and wheelbarrows.2. The bicycle uses human energy to paddle and move it.
Vehicles with Engines3. Many types of vehicles have engines which move them.2. The four-cylinder engine is commonly used in motor vehicles.3. A fuel is burnt in the engine to move the pistons. The up and down motion of the pistons causes the shafts in the vehicle to rotate and the wheels to turn. This makes the vehicle to move.
The Two-stroke Petrol EngineTwo-stroke Petrol Engine5. It is used for small machines e.g. motor boats, motorcycles and lawn mowers.2. It is an inlet tube for the petrol-air mixture to go in and an outlet tube for exhaust gases to up escape.3. The inlet tube and the outlet tube are open or closed by the piston moving up and down.
Upward stroke1. The piston moves up the cylinder.2. The inlet tube opens and the petrol-airmixture enters the cylinder due to lower pressure in the cylinder.3. Piston closes the outlet tube.4. Petrol-air mixture above the piston is compressed by therising piston.Downward stroke1. When the piston reaches the top of the cylinder, a spark fired by thespark plug ignites the petrol-air mixture in the upper part of thecylinder.2. The force of the expanding gases pushes the piston down, openingthe outlet tube and allowing the exhaust gases to escape.3. The piston closes the inlet tube as it is moving down and forcespetrol-air mixture into the upper part of the cylinder through a transferpassage.
Relationship between Operation of the engine and motion of the VehicleTransfer of Motion in a Car5. When the engine of a car is started, the pistons move up and down and rotate a crankshaft.2. When the gear is engaged, the crankshaft is connected to the transmission system (clutch and gearbox) and a drive shaft.3. The rotating crankshaft rotates the drive shaft, the differential gear, and the wheel axle, causing the wheels to turn.
The Gear SystemLow gear (force multiplier)5. When a low gear is used, a small gear (driving wheel) is used to turn a large gear (driven wheel).2. The large gear turns more slowly but exerts a greater force.3. A low gear is used when the car is starting to move or going up a deep slope.
High gear (speed multiplier)1. When a high gear is engaged, a large gear (driving wheel) is usedto turn a small gear (driven wheel).2. The small gear rotates faster (more speed) but has less force.3. A high gear is used to increase speed.
Clutch, Foot Brake and Accelerator1. The clutch is used when the driver wishes to change gear.Modern cars have an automatic system for changing gears.2. The foot brake is used for slowing down or stopping the car.3. The accelerator is used to increase fuel to the engine and soincreases the speed of the car.
Speed, Velocity and AccelerationSpeed = kelajuan
InertiaWhat is Inertia?5. Inertia is the tendency of a body to maintain its state of rest or uniform motion in a straight line unless it is acted upon by a force.2. Any body with mass has inertia.
Stationary inertiaStationary inertia is the inertia possessed by a body at rest.(e)We need to use a force to push an object, because the object’s stationary inertia resists motion.(b) When the cardboard is hit out of its position quickly, the coin falls into the glass. The coin tends to remain at rest in its original position because of its stationary inertia.(c) When block R is hit out of the stack quickly,P and Q move down vertically due to their stationary inertia.
Moving inertiaMoving inertia is possessed by a moving object. It resists any force trying to slow it down, make it go faster or change its direction of motion.(e)When a moving car stops suddenly, the passengers in the car are thrown forward because the moving inertia in the passengers continue to move them forward.(b) When an electric fan is switched off the blades continue to rotate for some time due to the moving inertia of the rotating blades.(c) Trains, cars, aeroplanes and ships which are moving cannot stop at once when the brakes are applied or the engines are switched off. They continue to move for some distance before stopping because of their moving inertia.
Relations between Mass and Inertia3. The tin with the bigger mass (tin filled with sand) requires a larger force to make it swing or to stop it from swinging.2. This shows a body with a large mass has more inertia than a body with a small mass.
Safety Measures Used in Vehicles to Reduce the Negative Effects of Inertia3. Seat belts prevent the driver and passengers from being thrown forward in a collision.2. Air bags prevent injury to the driver.3. The collapsible steering column prevent injury to the driver.4. Headrests prevent the heads of passengers from being jerked backwards.5. Bumpers in the front and the back absorb the collision force.6. The strong body frame of the car protects the passengers.
Applications of Momentum3. A falling pile driver has a large momentum because of its huge mass and high velocity so that it can hit a concrete pillar into the ground.2. A bullet fired from a gun has high penetrating power because of the high velocity of the bullet.3. A steam roller has a large momentum for rolling a surface because of its huge mass.
4. Gases escaping backward from a rockets (action)creates a forward momentum (reaction) which pushesthe rocket forward.5. A motor vehicle has safety features to protect thedriver and the passengers from the effect of the carshigh momentum in case of an accident
Principle of Conservations of MomentumConservation of Momentum4. When two or more bodies collide with one another, the total momentum before the collision is equal to the total momentum after the collision.Total momentum before collision = Total momentum after collision2. In an elastic collision the bodies separate after collision.3. In an inelastic collision, the bodies stick together after collision.
Worked exampleTrolley A collides with trolley B. After the collision thetwo trolleys become attached and move together.Calculate the velocity of the joined trolleys.
Experiment on Conservation of Momentum3. When match sphere P is pulled aside and released, it swings back, hits sphere Q and stops.2. The momentum of P is transferred to Q. But Q cannot move because it is sandwiched in the middle.3. So the momentum of Q is transferred to sphere R.
4. Sphere R swings outwards at the same velocity assphere P.5. This process is repeated with P and R swingingalternately, until the energy of the swinging spheres islost due to resistance and friction with the air.6. A Newton’s cradle usually has four or five metalspheres.
Applications of Pressure3. Some tools are designed to exert a large pressure by having the force act on a small area (Table A).2. Some gadgets and machines are designed to reduce the pressure on a surface by having the force act on a large area (Table B).
Principle of the Hydraulic SystemTransmission of Pressure in a Liquid1. Pascal’s PrincipleThe pressure exerted on a liquid in an enclosed containeris transmitted equally through the liquid in all directions.2. This principle is used in the hydraulic system.
The Hydraulic Brake3. When the driver’s foot pressses on the brake pedal, the pressure exerted on the brake fluid is transmitted unchanged to the four wheel cylinders.2. This pressure acting on a large of the piston in the cylinder produces a large force on the piston.3. This force pushes the brake pads outwards to press on the rotating drum or rotating disc and slow down or stop the motor vehicle.
The Hydraulic Jack3. A hydraulic jack uses a small force to lift a compressor very large force such as a motor car.2. When the compressor is switched on, the air pressure on the small cylinder, causing the large piston to rise.3. The pressure on the oil in the small piston is transmitted unchanged to the large cylinder4. This pressure acting on a large surface of the large piston produces a big force which pushes the car up.
Motion of Vehicles in WaterPrinciple of Operation of Vehicles in WaterVehicles without engines7. Sampans and canoes are moved through water by using human energy.2. Sailing ships are moved by using the kinetic energy of wind.
Ship3. A ship is driven by an engine which turns the propellers.2. The turning propellers push the water behind (action) and causes a forward momentum (reaction) which drives the ship forward.3. The rudder of the ship controls the direction of motion of the ship.
Hovercraft2. A hovercraft moves on a cushion of air on the surface of the sea.2. The engine turns the fans which produce the cushion of air to lift the hovercraft from the sea.3. The large fans on top of the hovercraft produce a strong backward wind (action) which causes an equally strong forward momentum in (reaction) that pushes the boat forward.
Hydrofoil2. The lower surface of a hydrofoil has wing-shaped structures called hydrofoils.2. At a certain speed, the hydrofoils get lifted above the water surface (aerofoil principle) and the boat moves faster because of reduced friction with the water.
Archimede’s Principle3. When a body is immersed in a fluid (gas or liquid), it experiences a loss in weight (up-thrust) equal to the weight of the fluid displaced by the body.2. When the ballast tanks of a submarine are filled with sea water, the submarine becomes dense and submerges in the sea.3. When the ballast tanks are emptied, the submarine becomes less dense and rises to the surface of the sea. This is because the weight of the submarine is now equal to the upthrust
Motion of Vehicles in AirThe Jet Engine4. Air is sucked from the front of the engine into the compressor and compressed so that it contains more oxygen for its volume.2. The hot compressed air is directed into the combustion chamber where a fuel such as kerosene is sprayed into it.
3. The mixture of hot air and fuel burns and releases hotexhaust gases, which escape from the back of the engineand produce a great backward momentum (action).4. This action causes as equally large forward momentum(reaction) which pushes the jet plane forward.
The Rocket Engine1.Liquid hydrogen and liquid oxygen are carried in therocket engine.2. The hydrogen fuel burns fiercely in the oxygen in thecombustion chamber producing exhaust gases.3.The exhaust gases escape from the back of the enginewith great backward momentum (action).
4. This action causes an equally powerful forwardmomentum (reaction) which pushes the rocket upwards.5. Unlike a jet plane, a rocket can move outside theEarth’s atmosphere because it carries its own hydrogenand oxygen.
Bernoulli’s Principle and Its Application in Aircrafts Bernoulli’s Principle