Tag Archives: motion

Power

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

Or

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.

Solution:

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.

Light-Bulb

P = Voltage*Current

Facts

  • 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.

Work

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.
boy-kicking-a-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.
worker-draging-load

Solution:

Applied Force = 50 N

Distance covered = 100 meters

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

Facts

  • 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.

Energy

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.

Facts

  • 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.

Laws of Motion

Man lifting a boxIn everyday life, we walk, drive cars, and lift objects. All these tasks need a force to be performed. So, it is necessary to understand this force scientifically. This force was described scientifically by Isaac Newton. He described the force and its relationships in his laws that are known today as the Newton’s Laws of Motion.

First Law of Motion

The first law states that an object in motion will continue to move with same speed in the same direction until another force acts on it. Furthermore, an object which is at rest (not moving) will not move until some external force acts on it.
velocity of car

You may be thinking, how this is possible. Because as you kick a ball, it will immediately start to slow down and will come to rest at a distance. This happens because of air friction. As you kick a ball, frictional forces immediately start to oppose the motion of the ball until it comes to rest.

Second Law of Motion

boy-kicking-a-ballThe Second Law states that force is equal to mass times the acceleration. Let’s say it in other words, the more force is applied to an object the more acceleration will be produced in it. As a result, the object will speed up faster. For example, if you hit a ball harder, it will go faster and farther.

The Second law of motion can also be defined in the mathematical form. It is defined as, F = mass * acceleration.

F = m*a; m is the mass and “a” is the acceleration

Third Law of Motion (Every action has reaction)

You may be familiar with the statement of this law which states that “every action has equal and opposite reaction”. In other words, each applied force also has the opposing force, which has the same magnitude of applied force but in opposite direction. For example, when you kick a ball with 10 N force, your feet will also experience the same 10 N force from the ball.

Facts

  • First law of motion also tells us that, mass has a resistance to change in motion. This resistance is called inertia.
  • Sir Isaac Newton is also the founder of Calculus; a branch of mathematics which deals with the rate of change.
  • An object in motion experiences friction from the ground and air. Friction also helps our cars to slow down, when the brakes are pressed.

Force

What is Force?

lifting forceEverything you see around yourself is surrounded by forces. These force may be push-pulls or gravitational. Forces can accelerate, slow-down, and change the shape of an object. So, what is the definition of the force? Force is actually an interaction which when applied to an object, changes or tends change it state of motion or rest. In other words, force can bring the objects that are not moving into motion. Similarly, it can bring the moving objects into the full stop.

Force is a vector quantity, that means it requires magnitude along with a direction in which the force is applied.

How is Force Calculated?

Force is measured in newton, abbreviated as “N”. One newton is equal to a force, which when applied to an object having a weight of 1 kg, accelerates it to 1 m/s^2. That means, if you constantly apply one newton force to a 1 kg heavy object, its velocity will increase by 1 meter per second in each passing second until you remove the force.

Force is calculated by using the Newton’s second law of motion:

F = m*a

Here “m” is the mass of the object and “a” is the acceleration of that object.

Example: A bike has a mass of 100 kg which is accelerating with an acceleration of 5 m/s^2. Calculate the force that is acting upon it.

Solution:

You are given the mass of the bike and acceleration of the bike. Just apply the Newton’s second law of motion.

F = m*a = 100*5 N = 500 N

Types of Force

There are various types of force, according to their nature. Few most familiar types of force are:

  1. Friction: It is the force which opposes the motion of an object. When you kick a box, it will come to rest at a certain It is the friction that is slowing down the box. Friction only acts on the moving objects.
  2. Gravitation: Gravitation is an attractive force that is caused by heavy objects, like planets. This force attracts anything that has mass. You are standing on the Earth due to the gravitational force of the Earth.
  3. Tension: It is the pulling force which is exerted on strings, cables or any similar object like them.

Facts

  • Torque is kind of force that rotate or twist the objects.
  • Gravitational and electromagnetic forces don’t need to have a contact with the object for exerting force. They can exert a force on objects which are away from them.
  • Force was described by the Isaac Newton in his law called Newton’s second law of motion.