Understanding Bernoulli's Principle

Have you ever thought why birds can fly so efficiently in the air?or likewise the plane?

that movement or phenomenon can be explained by Bernoulli's Principle.

Bernoulli's Principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases.

Therefore, the pressure in a moving fluids depends on its flow velocity (remember fluids = water, air)

A full definition of Bernoulli's Principle is:

IN a steady flow of a fluid, the pressure of the fluid decreases when the velocity of the fluid increases.

Bernoulli's principle is very important as it is used in the design of airplanes, boat hulls, fan blades and cars.

Example of situations that involves Bernoulli' s Principle:

Ping Pong Balls and Funnels

An inverted filter funnel can hold a ping pong ball if you blow air through the funnel, it does not drop down. Thats because the air flows around the ping pong ball at high speed and creating  a low-pressured area, the higher atmospheric pressure supports the ball from falling.

Curve Balls in Baseball

Now lets move on from ping pong to baseball. A pitcher occasionally tries to fool the batter into a strike by throwing a curve ball. It seems to be heading straight into the strike zone but veers off at the last minute. STRIKE! How do they do that?

Specific Heat Capacity

Specific Heat Capacity

1. Specific heat capacity, c, of a body is the heat that is needed to increase the heat of a unit of mass or the substance by 1°C or 1K.2. The unit of specific heat capacity is Jkg-1°C-1.3. For example, the specific heat capacity of water is 4200 Jkg-1°C-1 . This means that 4200J of heat is needed to increase the temperature of 1 Kg of water by 1°C.4. Therefore, when a body of a mass m and specific heat capacity, c, absorbs a quantity of Heat, H, then its heat will increase by θ.5. Therefore H = mc θ.6. On the contrary, when the heat of a body falls by θ, the quantity of heat that disappears (lost) is also H = mc θ.7. The specific heat capacity is dependent upon the type of substances. Different substances have different specific heat capacity.8. By knowing the specific heat capacity, we can determine the mass and also the change of temperature of a body if we know the amount of heat that is transferred.9. Total heat transferred H = mc θ.10. Generally, liquid has more specific heat capacity than solids. This means that liquids need more heat energy than solids for the same rise in temperature.

Specific Latent Heat

The specific latent heat of a substance is the energy which is required to change 1 Kg of a substance from a certain physical condition to another physical condition without any change in temperature.

The unit for specific latent heat is JKg-1.

The graphs above shows how the temperature of a quantity of substance such as water changes over time when heat is supplied to it.

All along the temperature from 0 to 273 K, water is in the form of solid, that is ice.In this phase:- When the temperature is raised, the water molecules vibrate even faster.- Heat energy supplied is converted to kinetic energy.

All along the straight line at 273K, a change of phase from ice to water occurs.As:- Even though heat is still supplied to it, the temperature does not increase all along.- This is because the heat energy supplied is needed to separate the water molecules and not for the increasing their energy.- The heat that is required in the change of phase from Solid to liquid is termed the latent heat of fusion.

At the end of the straight line at 273K, all of the solid (ice) has melted into liquid.

All along the graph from 273K to 373K, water only exist in the form of liquid only. Therefore, the temperature of water will increase when heat is supplied to it.

All along the graph of 373 K (the level phase), the change of phase from liquid to gas occurs.Along the line:- Water is boiling.-it is observed that the temperature does not change even though heat is constantly supplied to the substance.- Heat is required to separate the water molecules and to do the work of opposing air pressure when the liquid changes into gas.-The heat required to convert liquid into gas is termed the latent heat of evaporation.

At the end of the level line at 373K, all of the liquid has been changed into gas.

At the graph from 373K to 473K, water is in the form of gas and the temperature rises when heat is supplied.

When there is cooling, the reverse process occurs.

Latent heat of fusion and latent heat of evaporation will be released.

Since the heat energy supplied during the change in phase cannot be detected by a thermometer, this type of heat is referred to as latent heat.

Therefore, the change of state is an 'energy change without any loss of temperature change' phenomenon.

Specific Latent Heat of Fusion

Specific latent heat of fusion, L of a substance is the quantity of heat which is required to change one unit mass of the substance from solid to liquid without any change of temperature at the melting limit.

Its unit is JKg-1.

This condition occurs at the melting point of the solid.

For example, 336000J of heat is required to change 1Kg of ice at 0°C.Therefore the latent heat of fusion, L for ice is 336 000 JKg-1.

when liquid solidifies, the specific latent heat of fusion will be released.

This condition occurs at the freezing limit of a liquid.

For example, when 1 Kg of water at 0°C solidifies to become 1 Kg of ice of 0°C, 336 000 J of heat are released.

If m Kg of solid or liquid is involved, the quantity, Q of heat absorbed or released is Q = mLwhere Q = quantity of heat that is absorbed or releasedm = mass of substanceL = latent heat of fusion

Below are examples of substance with its specific latent heat

Aluminum 3.96x105 JKg-1. Copper 2.05x105 JKg-1. Iron 2.67x105 JKg-1. Lead 0.23x105 JKg-1. Brass Unknown  Magnesium 3.7x105 JKg-1. Zinc 1.1x105 JKg-1.

Understanding the Reflection of Light: Law of Reflection of Light

1. The reflection of light can be studied by using light ray(s) and a plane of mirror which is placed on a piece of white paper.

image from: http://www.hsphys.com/pmirrb.jpg

2. When the ray of light is incident onto the surface of a plane mirror, the light ray does not pass through the mirror but it reflected back by the plane mirror.

3. The phenomena of ths experiment shows the phenomena of reflected light.

The Law of Reflection of Light

1. The incident Ray, the reflected ray and the normal all lie in the same plane.

2. The angle of incidence is equal to the angle of reflection.

Applying Archimedes' Principle

Steel is denser than water. However they still float, why?

Have you ever wondered why hot air balloon floats in the air? Even though the mass of the balloon is big?

Archimedes (287-212 B.C.) was a greek scientist who first discovered that

"an object submerged in a liquid is acted on by an upward buoyant force (or upthrust)."

The buoyant force is due to the surrounding liquid which causes the object to weigh less in the liquid. Archimedes realised that submerged objects always displace liquid upwards, (when you put an ice to a glass of water, the water level rise). Later he did show that the upthrust is equal to the weight of water displaced.

Archimedes' principle states that an object, whether completely or partially immersed in a fluid, is acted on by a buoyant force, which is equal to the weight of the fluid displaced

Application of Specific Heat capacity

Application of Specific Heat capacity

1. Substances having a small specific heat capacity can be quickly heated up, it also experience a big change in temperature even though only small amount of heat is supplied.2. Substances having a small specific heat capacity, are very useful as material in cooking instruments such as frying pans, pots, kettles and so on, because, they can be quickly heated up even when small amount oh heat is supplied.3. Sensitive thermometers also must be made from materials with small specific heat capacity.4. Substances that have a high specific heat capacity is suitable as a material for constructing kettle handlers, insulators and oven covers, because, even when much heat is given it will only undergo a small changes in temperature.5. Heat storage instruments are very useful and they are usually made of substances with a high specific heat capacity.6. Water as a cooling agent acts excellent as a cooling agent in engines. Water is also used in houses in cold climate countries.

Car radiator

Water is pumped through the channels in the engine block to absorb heat. Water is used as the cooling agent due to its high specific heat capacity. The hot water flows to the radiator and is cooled by the air flows through the

fins of the radiator. The cool water flows back to the engine again to capture more heat and this

cycle is repeated continuously.

Cooking utensils

Cooking utensils are made of metal which has low specific heat capacity so that it need less heat to raise up the temperature.

Handles of cooking utensils are made of substances with high specific heat capacities so that its temperature won’t become too high even if it absorbs large amount of heat.

Thermal Radiator

Thermal radiators are always used in cold country to warm the house. Hot water is made to flow through a radiator. The heat given out from the

radiator is then warm the air of the house. The cold water is then flows back to the water tank. This process is repeated

continuously. Water is used in the radiator because it has high specific heat capacity.

Sea Breeze

Land has lower heat capacity than sea water. Therefore, in day time, the temperature of the land increases faster than the sea.

Hot air (lower density) above the land rises. Cooler air from the sea flows towards land and hence produces sea breeze.

Land Breeze

Land has lower heat capacity than sea water. During night time, the temperature of the land drops faster than the sea.

Hot air (lower density) above the sea rises. Cooler air from the land blows towards sea and hence produces land breeze.

Application of Archimedes' Principle

1. Submarine:

A submarine has a large ballast tank, which is used to control its position and depth from  the surface of the sea.

A submarine submerges by letting water into the ballast tank so that its weight becomes greater than the buoyant force (and vice versa). It floats by reducing water in the ballast tank.-thus its weight is less than the buoyant force.

2. Hot-air balloon

The atmosphere is filled with air that exerts buoyant force on any object.

A hot air balloon rises and floats due to the buoyant force (when the surrounding air is greater than its weight). It descends when the balloon weight is more than the buoyant force. It becomes stationary when the weight = buoyant force.

The weight of the Hot-air balloon can be controlled by varying the quantity of hot air in the balloon.

3. Hydrometer

A hydrometer is an instrument to measure the relative density of liquids.

It consists of a tube with a bulb at one end. Lead shots are placed in the bulb to weigh it down and enable the hydrometer to float vertically in the liquid.

In a liquid of lesser density, a greater volume of liquid must be displaced for the buoyant force to equal to the weight of the hydrometer so it sinks lower.

Hydrometer floats higher in a liquid of higher density.

Density is measured in the unit of g cm-3.

4. SHIP

A ship floats on the surface of the sea because the volume of water displaced by the ship is enough to have a weight equal to the weight of the ship.

A ship is constucted in a way so that the shape is hollow, to make the overall density of the ship lesser than the sea water. Therefore, the buoyant force acting on the ship is large enough to support its weight.

The density of sea water varies with location. The PLIMSOLL LINE marked on the body of the ship acts as a guideline to ensure that the ship is loaded within the safety limit.

A ship submerge lower in fresh water as fresh water density is lesser than sea water. Ships will float higher in cold water as cold water has a relatively higher density than warm water.

Understanding Thermal equilibrium

Temperature, Heat and Thermal Equilbrium

1. Temperature is one of the base quantities in physics.

2. Temperature is a physical quantity which measures the DEGREE of HOTNESS of an object. A hot object has a higher temperature than a cold object.

3. The SI unit of temperature is Kelvin, K. Other units such as Degree Celcius (centigrade) and Fahrenheit is also used.

4. When two objects are in thermal contact, heat is transferred from one object to the other.

5. The temperature of the objects determines the direction of energy transfer between them. The energy transferred between objects in thermal contact is known as heat.

6. Let say there are two objects A and B.

7. Say A has higher temperature than B. When A and B is in contact with each other, heat will be transferred from A to B. That is A will give heat and B will receive heat. When this situation occurs, it is called net heat transfer from A to B.

8. The heat transfer will continue until a state of thermal equilibrium is achieved.

9. It is expected that temperature of B will rise to a certain degree (due to increased kinetic energy in the molecules), when thermal equilibrium is achieved and temperature A will fall. At the end both A and B will have the same temperature.

10. Heat is a form of energy. SI unit for heat is joule, J.

11. Heat is produced by mechanical energy or from the conversion of other types of energy. such as electrical energy to heat energy and so on.

12. It must be noted that Temperature is NOT the same as Heat.

Temperature is a measure of degree of hotness of an object, is a base quantity, SI unit is kelvin and other units are degree celcius and fahrenheit. It determines the direction of heat flow.

Heat is a form of energy, is a derived quantity and SI unit is Joule, J. other unit is calorie, cal. It is being transferred from a region of higher temperature to another region of lower temperature.

Understanding Pressure

1. Pressure on an area, A is the normal force, F, whish is being applied perpendicularly to the area.

2. Pressure on an area, A is expressed as the normal force, F per unit area, A.

3. P = (F/A)

4. This SI unit for pressure is the pascal, Pa, where 1 Pa = 1 N/m2 (metre square).

5. Pressure is increased:

if the force, F applied to a given area, A is increased.

if a given force, F is applied to a smaller area, A.

6. If a balloon is pressed against by a finger, the balloon will only change its shape a bit. If the balloon is pushed against by a needle with the same force, the balloon will burst. This is because a finger has a larger surface area (A) than a needle. Hence, the needle exerts much pressure than the finger and perforates through the surface of the balloon and making a hole and freeing the air inside the balloon.

Applications of Pascal's Principle in Everyday Life

A hydraulic system is a device in which a small applied force can give rise to a larger force.

The principle in the hydraulic system is widely used in jacks, vehicle brake systems, hydraulic presses and heavy machinery.

Hyraulic JacksHydraulic jacks are used to lift a heavy load such as when changing a car tyre. When the handle is pressed down, a valve closes and the small piston forces hydraulic fluid through another valve to the larger cylinder. The pressure transmitted results in a large force on the load.

When the handle is raised, valve B closes and hydraulic fluid flows from the buffer tank through valve A into the small cylinder. The handle is moved up and down repeatedly until the load is sufficiently lifted up.

The large piston can be lowered at the end by opening the release valve to allow all the hydraulic fluid to flow back into the buffer tank.

Hydraulic Brakes

Hydraulic brakes are used in cars, lorries and motorcycles.

In a hydraulic brake system, a liquid, known as brake fluid,

is used to transmit pressure from the brake pedal to all the wheels of the vehicle.

When the brake pedal is pressed, the piston of the control cylinder applies a pressure on the brake fluid and this pressure is transmitted, via a system of pipes, to each cylinder at the wheels.

The cylinder at the wheels cause a pair of pistons to push a pair of friction pads to press against the surface of the brake discs or brake drums. The frictional forces between these brake components cause the vehicle to slow down and stop.

When the brake pedal is released, a spring restores the brake discs to their original positions.

Hydraulic Pumps

Hydraulic pumps are used to raise cars in a motor workshop.

The machine is equipped with a small cylinder connected to a large cylinder. Both cylinders are filled with oil.

Compressed air is introduced into the small cylinder in which the compressed air exerts a pressure on the surface of the oil.

This pressure is transmitted by the oil to the large cylinder where the pressure acts on a large piston to produce a force which is large enough to lift a car.

Charles' Law

Charles' Law can be explained by the kinetic theory of gases.

When the temperature of a gas is raised, the gas molecules will move more actively and with more energy.

The rate of collision of the gas molecules onto a unit area of the wall of the container will increase.

Each collision will also produce a greater force because the change in momentum for each molecule increases when its speed is higher.

To maintain the same pressure in the container, the volume of the gas will increase so that the above effects will be balanced by the effect of an even smaller number of molecules per unit.

Charles' Law states that for a mass of gas held at a fixed pressure, the volume of the gas is directly proportional to the absolute temperature of the gas.

According to Charles' Law

V1/T1 = V2/T2

V1 = initial volumev2 = final volumeT1 = initial temperature in KelvinT2 = final temperature in Kelvin