An experiment to show that the vertical and horizontal motions of a body are independent of each other
Place two coins A and B near the edge of a table as shown in the figure. Simultaneously drop the coin A vertically and flick the coin B horizontally. After a while we will hear just one clink, showing that both the coins reach the ground at the same time. This means that both the coins are thrown from the same height, take same amount of time to travel the vertical distance from the table to the ground. From the above experiment we conclude that in any given time interval, the vertical distance travelled by an object thrown horizontally is the same as that travelled by an object dropped vertically from the same height. This is shown more clearly in the figure given below.
When the card is flicked with the finger the coin placed over it falls in the glass
But the horizontal distance travelled by a projectile depends upon its velocity in the horizontal direction.
The horizontal distance travelled by a projectile depends upon its velocity in the horizontal direction
The higher the velocity with which a projectile is projected horizontally greater is the horizontal distance travelled by the projectile. The time taken by a projectile to fall through the height h can be obtained as follows,
For a body released from a height h, s = h, u = 0 and a = g
From the above equation it is clear that the time taken by a body falling under gravity to travel a distance h depends only upon the value of g at that place. The horizontal velocity of the body falling under gravity has no effect on the time taken to travel through a certain height.
All projectiles follow a curved path which is bent towards the Earth. The horizontal distance travelled by a projectile depends upon the horizontal velocity with which it is thrown. So, if a projectile is projected with a very small horizontal velocity then it will definitely hit Earth's surface which is also curved. However, when a projectile is thrown with a very high velocity it does not hit Earth's surface and it may start revolving around the Earth in a fixed orbit.
How does a projectile become a satellite
Problem
1. A body weighs 12 kg on a weighing machine on the Earth. If it is taken to the moon, will the weighing machine show any change in reading? If so what is the weight of the body on moon.
Solution:There will be a change in the reading shown by the weighing machine.
Weight of the object on moon (Wm) = mgm.where 
is the acceleration due to gravity on moon,
Solution:
Weight of the body on Earth (We) = mge.
Summary
- Mass is defined as the amount of matter contained in it.
- SI unit of mass is Kilogram.
- Mass remains constant throughout the universe.
- Mass of an object can never be equal to zero.
- Mass is a scalar quantity.
- Weight is the force with which an object is pulled towards the centre of the Earth.
- SI unit of weight is Newton.
- W= mg.
- Weight is a Vector quantity.
- Weight of an object can be equal to zero i.e., when g is equal to zero.
- Weight varies from place to place.
- 1kg.Wt = 9.8 N.
- Projectile is an object thrown into space horizontally under the action of Earth's gravity.
- Trajectory is the path followed by a projectile.
Effect of gravity on plants
Just as we are affected by gravity, plants also respond to gravity. Most of the plants being fixed at one place, their movements take place by bending their parts and are called curative movements. The movement of curvature in response to gravity is called geotropic movements and this phenomenon is called geotropism.
The stem is negatively geotropic while the roots are positively geotropic.These movements can be studied best when germinating seeds are kept in different directions.
