Our world is surrounded by forces. All these are either pushing or pulling forces. Not only the force of gravity pulls everything on earth towards the centre of the earth, but also it keeps our planet Earth in orbit around the Sun.
Thanks to friction we can walk and drive without slipping or skidding. Things which are light in weight can float on water, because of upthrust. Magnetic force, surface tension and electric force are some other types of forces in our environment. So now, let’s learn about these forces in detail.
A force is a push or pull. A force makes something move.
Examples of forces – push and pull
Forces can make things change shape, change direction, change speed.
To stretch a chest expander or squash a can out of shape, a big enough force produced by a strong man is needed.
A car begins to move using the force produced by the car engine and gradually it speeds up. When you apply the brakes you can slow it down, and then stop it. This means the force produced by the brakes has slowed down the car’s wheels.
You have to pedal a bicycle harder by using more force, if you want to go faster.
How do you play football?
You have to kick the ball when you play football. Here, you use the pushing force to move the ball forward with your foot.
The harder you kick the ball, the faster it will move. How fast the ball goes depends on the strength of the kick.
A force can change the direction of something that is moving.
A tennis player puts a force on the moving ball, which is travelling towards him, by hitting it with the racquet. The ball changes its direction by moving away from the racquet in a different direction.
Similarly, a cricketer or baseball player hits a ball that is moving towards them. The ball then changes direction and moves away from them. Which way the ball goes depends on the direction of the hit.
Using an arrow you can show which way a force is moving and how strong it is.
A twist is a force that makes something move in a circle. Twisting the lid of a jar or bottle opens the jar. Twisting it the opposite way closes it.
Sometimes more than one force acts on an object at the same time. When people push or pull in the same direction, their forces add together to give a much bigger force.
Two forces can help each other. It’s difficult to move a car by pushing it yourself. It’s easier if a friend helps you to push in the same direction.
But if two forces are acting against each other, the largest force will win.
Two forces can work against each other. That’s what makes a tug of war so tiring. Your team pulls one way. The other team pulls in the opposite direction. If one team’s force exceeds the other team’s force, the team with the highest force can pull the other team towards them and win the game.
There is no movement in either direction as long as both teams pull with the same force. This is where two forces are equal. When this happens, the two forces balance each other.
The floating toy duck
When you put a toy duck made of rubber or plastic into water, it will float on water.
So, how this toy duck floats on water?
The force of the water pushing the toy duck up is equal to the force of gravity pulling it down.
Types of forces around us
Following is a list of examples of forces which act on or around us.
Force of friction
Things which are moving will slow down because of the force of friction. Whenever two surfaces rub on each other a force of friction is produced. Friction always works in the direction opposite from the direction the object is moving or trying to move.
Gravity pulls everything downwards. This means gravity pulls everything towards the centre of the earth. Everything on Earth, and on other planets, is affected by the force of gravity.
A rubber or plastic ball floats on water. A force called upthrust keeps the ball up. This force is produced by water pushing on the ball from underneath.
Gases and liquids can both supply upthrust. When you release a hydrogen balloon it rises, because of the force upthrust.
Things that have iron, steel, cobalt, or nickel in them are magnetic, because they are attracted to the magnet by a magnetic force.
A raindrop keeps its shape when it lands on a waterproof surface. That’s because of surface tension. The water molecules attract each other strongly and form a kind of skin on the water surface.
You can even float a pin on water. If you lay a pin carefully on the surface of water; surface tension keeps it up.
Have you ever tried picking up pieces of paper with a plastic pen?
To do this first you have to rub the plastic pen on a duster. Rubbing gives the plastic an electric charge. This electric force pulls the paper to the pen.