Tag Archives: physics


In our everyday life, we tell the hotness and coldness of different substances and weather in terms of temperature. We also use temperature to find the severity of the fever. For example, our normal body temperature is 98 ⁰F. This temperature increases when we caught in the fever. We also set our oven and electric stoves at a certain temperature to cook food.temperature

What is Temperature?

We use temperature to describe the hotness. But in physics, temperature is defined as the average kinetic energy of molecules in a substance. If the temperature of a substance is more, then its molecules will have higher kinetic energy.

How temperature is measured?

Temperature is measured with a device called thermometer. Thermometer works on the principle that, when the temperature of a substance rises they expands. Some materials, like mercury and alcohol expands more, so they are used in the thermometers. However, electronic and infrared thermometers are also developed. They use special sensors to measures the temperature instead of mercury or alcohol.

Temperature scales

There are various units to measure the temperature of a substance. These units are Celsius, Fahrenheit, kelvin, and Rankine.

  1. Celsius: Celsius is widely used unit in the world. It measures the temperature in degrees, abbreviated as ⁰C. This temperature scale measures the freezing point of water at 0 ⁰C and boiling point at ⁰C.
  2. Fahrenheit: Fahrenheit is famous in US and it is also used by doctors. This temperature scale measures the freezing point of water at 32 ⁰F and boiling point at 212 ⁰F.
  3. Kelvin: This scale is also considered as absolute scale and is mostly used by scientists. This scale is not measured in degrees and is abbreviated as, K. The zero point is set at the absolute zero; the temperature at which average kinetic energy of a substance is zero. The freezing point of water is measured at 273 K, and boiling point at 373 K.
  4. Rankine: Rankine is not used very much today. The zero of this unit is also at absolute zero. This scale is measures the temperature in degrees and is abbreviated as, ⁰


  • The scale Kelvin was founded by Lord Kelvin. He Proposed the unit on the basis of absolute temperature of a substance.
  • The first thermometer was invented in 1600s and was called thermoscope.
  • Electronic thermometers use the electrical property of substances to measure the temperature.


When winter arrives, we all prepare our heating system which includes an electric heater, coal heaters, or gas heater. These heaters provide us heat in winter so we can warm up our bodies. Also, we use heat for cooking our food. Sometimes excess heat disturbs our living, so air-conditioners are used to remove that excess heat.

What is heat?

Heat is actually a kind of energy transfer from one object to another, when there is a temperature difference between them. Heat always flow from hot object to cold object. Don’t confuse yourself with heat and temperature, they both are separate quantities. Heat is measured joule; the unit in which energy is measured. Whereas, temperature tells, how hot a substance is?

Heat is measured in joules; the same unit of energy measurement. There are other units for measuring heat, which are BTU (British Thermal Unit) and calorie.

Heat transfer

Heat can be transferred in several ways. There are three methods in which heat can be transferred. These methods are:

  1. Conduction: Conduction takes place when two objects are in contact with each other.
  2. Convection: In this methods, heat is transferred by flow and diffusion of liquids from high-temperature regions towards low-temperature
  3. Radiation: In this method, heat is transferred by radiation e.g. visible light and infrared rays.

Read more about Heat transfer in our article: Heat Transfer

Effect of heat on states of the matter

As the heat of an object increase, its temperature also increases. Each type of substance has a certain value to remain in its particular state (solid, liquid, or gas). When temperature increases or decreases from these values the state of the substance is changed. For example, water turns into ice when the temperature drops below the 0 ⁰C. When the temperature reaches 100 ⁰C, the water starts to boil and is converted into steam (gaseous state of water).

Note: Pressure of the atmosphere also affects the state of the substance.


  • A substance containing more heat does not always mean that its temperature is also high.
  • A cup of tea at 50 ⁰C has a lot more heat than a drop of water at 99 ⁰
  • Each material has a certain capacity to hold the heat at a particular temperature. It is called the heat capacity.
  • A cup of water at 99 ⁰C will not warm up the bucket of water. But, another half filled bucket at 60 ⁰C can warm up the water in the first It is because half filled bucket has more heat than the cup of water at 99 ⁰C.


What is Power?

crane-powerIn physics, power is the rate of doing work. Because work does not deal with time, it only tells us that how much energy is consumed in performing the work. Since the same work can be done at different rates. For example, you and your friend are pushing the boxes having the same weight. Now, your friend reaches the target in 60 seconds and you reach the same target in 100 seconds. Both of you have expanded the same amount of energy to push the box. But, your friend did the work faster than you, so its power was more than you.

How is Power measured?

Power is measured in watts in the international system of units. One watt of power is equal to one joule energy expanded in one second. The mathematical formula for calculating the power is:

Power = Work/time


P = W/t

Example: Two persons are carrying boxes towards their home. The first person is reaching the home in 100 seconds, whereas the second person in 40 seconds. Calculate the power of both persons, if the work performed by both is 400 joules.


Power of the first person is:

P1 = work / time = 400 joules / 100 seconds = 4 watts

Power of the second person:

P2 = work / time = 400 joules / 40 seconds = 10 watts

Clearly, the second person is doing the work with more power than the first person.

The power is also measured in another unit, which is called horsepower. Horsepower is bigger unit than a watt and is mostly used for heavy duty machines. One horsepower is equal to 745.7 watts.

Electrical Power

Our rate of electricity consumption is also measured in watts. To find out how much power we are using, just multiply the current flowing in the circuit with the voltage of the circuit.


P = Voltage*Current


  • Chemicals that release energy very fast result into the explosions.
  • Your electricity bill is calculated in kilowatt-hours. This is the unit of energy, not the power.
  • In real practice, machines with high power consume more energy than the machines with low power to perform the same Because increasing power can decrease the efficiency.


You might think about work as, reading books and doing homework. You may have also heard the sentence “hard work leads to success”. But, in physics work has its own meaning and it is different from the previously described example.

What is Work?

In physics, work is done when a force is applied to an object and it travels some distance. For example, you kicked a ball with a certain amount of force and ball traveled few meters, then you had done a certain amount of work on the ball.

How is Work measured?

Work is the scalar quantity, means it doesn’t need direction to define it. Work is measured in joule or newton-meter. This is the same unit in which energy is measured. The work done on an object is found by multiplying the force exerted on an object with the distance that it traveled.

Work = Force*distance

But, there are also some complications in calculating the work which may sometimes confuse you. Here are the few things to remember when calculating the work.

  1. If you are applying a force on an object but it is not moving, then work will be zero. Because object didn’t travel any distance. For example, you are pushing a wall with all of your force, but the wall is not moving. So, your work done will be zero.
  2. If you are applying a force on an object and it is moving in a path that brings it back from where it started. Then, work done on that object is also zero. Because the net distance traveled by the object is zero. For example, a race car is starting from a starting point and traveling in a circular path and it comes back again at the same starting point. Then, work done by the car is zero because it didn’t travel any net distance.

Example: A man is pushing a box with a force 50 newtons. The box has traveled the distance of 100 meters. Calculate the work done by the man.


Applied Force = 50 N

Distance covered = 100 meters

Work = Force*distance = 50*100 = 5000 joules or N-m


  • If a force is applied in opposite direction to the covered distance, then the work is said to be negative work.
  • An object that falls from a height also performs work due to gravitational force and height.
  • In space when an object is accelerated to a certain speed then the force is removed from it. But, the object doesn’t lose its speed because there is no any air friction in space. So, work done by objects flying in space is also zero.


What is Energy?

energyThe ability to do work is known as energy. Anything that is doing something uses energy. Your body needs the energy to walk, think and lift your school bag. We get this energy from our food. All the mechanical objects such as cars, bikes, buses, and airplanes need some kind of energy source like gasoline to do their work.

Energy is measured in joules in the international system of units. But, there are also other units of energy like kilowatt-hour. This unit is mostly used is your home’s electricity meters. Your electricity bills are calculated according to the usage of energy in kilowatt-hour.

Types of Energy

There are many forms of energy including chemical, electrical, heat, light, kinetic, potential and nuclear energy. These different energy forms can be converted into each other. For example, we use electric heaters in winter to warm up our homes. These heaters use electrical energy and convert them into the heat energy. Let’s dig into each type of energy.

  • Chemical Energy: It is stored in the bonds of molecules. When chemical reaction happens, they release chemical energy. We use chemical energy in our car in form of gasoline to drive. Batteries also use chemical energy to produce electricity.
  • Electrical Energy: It is the widely used form of energy. Today it is very difficult to think about life without electricity. We are almost doing every work with electricity. Electrical energy is obtained from the movement of electrons. It is mostly produced from fossil fuels like coal and gasoline.
  • Heat Energy: We use this energy to cook our food and heat our homes during winter. Heat energy is obtained from molecules at high temperature. For example, electrical or gas stoves are used to heat up the pots for cooking food.
  • Light Energy: Light energy is the form energy that we are able to see. Our Earth receives a lot of light from the Sun. Light is also produced by electricity at homes. We can also generate electricity from light by using Photovoltaic cells.
  • Kinetic Energy: Kinetic energy is also known as the energy of motion. If an object is moving, it has kinetic energy. Cars moving on roads have kinetic energy due to their motion.
  • Potential Energy: Potential energy is also called stored energy. Energy stored in springs is potential energy. Also, objects at heights have also potential energy due to the gravity. This energy is released when objects fall.
  • Nuclear Energy: This energy is released during a nuclear reaction; fission and fusion. Nuclear reactions release a huge amount of energy. Many power plants across the globe utilize fission reaction to generate electricity.

Renewable and Non-renewable Energy

Energy is classified into two types, one in renewable energy and the other is non-renewable energy. Renewable energy is the types of energy whose resources are not consumed up and can be recycled. Examples of renewable energy include solar energy, wind energy, and geothermal energy etc. Non-renewable energy sources are consumed in the process and can’t be recycled. Examples of this types of energy include coal and gasoline.


  • People have been using wind energy for more than a thousand year.
  • One lightning bolt can power a 60 watts light bulb for six months.
  • Geothermal power plants are used to generate electricity by using the Earth’s internal heat.