A force can change the state of motion of a body. Force can either stop a moving object or make a stationary object start moving.
a) A goal keeper saving a goal. A goalkeeper can stop the moving ball by applying a force.
b) Hockey player flicking a ball. The ball that is already moving moves faster after the hockey player flicks the ball and the direction also changes.
The speed and the direction of motion of a body is described as its state of motion. The state of rest is considered to be the state when the body is at rest or called state of zero speed. An object might be at rest or in motion; both are its states of motion.
The force will cause the object to come to a stop after sometime.
When the force acts on a moving object in the same direction as its motion, the object's speed increases as the force adds to the already existing force on the object.
No. that’s not it. To change the state of motion of a body the force acting on the body has to be more than the resultant of the force acting previously. Additionally, force acting on a body has lots of other effects such as, change in shape, change in direction etc.
Examples of change in shape of an object are as follows:
• Squeezing of a plastic bottle
• Deformation of clay when pressed between two hands
Following are the different effects of forces on an object:
• Change in the state of motion
• Change in the direction of motion of an object
• Change in the shape of an object
• Turn or spin of an object
The application of force by the hockey stick on the ball results in a change in direction of motion of the ball.
Peter uses muscular force to hold the bucket of water above the ground. The muscular force acts against the force of gravity that pulls the bucket towards the ground. Peter’s muscular force and the gravitational force are equal in magnitude but opposite in direction. Therefore, the net force on the bucket is zero. Hence there is no change in its state of motion.
The force exerted by a charged body on another charged or uncharged body is known as electrostatic force. An example of an electrostatic force is the force resulting when two balloons are rubbed against one another.
The force resulting due to the action of muscles is known as muscular force. We apply muscular force to lift objects.
The force that acts on all moving objects in a direction opposite to the motion of body is called the force of friction. Birds and fish have streamlined bodies to reduce the respective air and water resistance that they feel.
Friction comes into play only when there is contact between two surfaces. That is why it is called a contact force.
An object can either be in rest or in motion. A force can be applied on an object to stop its movement, if it is in motion or to make it move if is at rest.
Gravitational force is the natural force of mutual attraction between all physical bodies in the universe.
The pressure exerted by the air around us is known as atmospheric pressure.
The sucker is designed in such a way that when pressed against a smooth surface, the air is forced out from beneath the sucker. Since the air pressure outside is greater than the air pressure beneath the sucker, it results in a tight contact that does not break easily.
The rubber sucker is unable to make an air tight seal as rough surface, since the rough surface allows gaps through which air can enter and leave. Hence, the pressure outside is the same as inside and the sucker does not stick to the surface.
The thick rounded piece of cloth increases the area of the surface in contact with the luggage and hence the pressure on the porter’s head due to the luggage is considerable reduced.
School bags carry lot of load and hence the bag is heavy. The straps are made wide so that the weight of the school bag acting downwards is effectively distributed over a large area and thus, the pressure on the hand or shoulder is reduced.
Snow shoes have large flat soles and hence the weight of the body is distributed over a large area. Thus, the pressure exerted on the snow is reduced and our feet do not sink too much in the snow.
The weight of air in a column of the height of the earth’s atmosphere and area 100 cm2 is as large as 1,000 kg. We are not crushed under this weight because the pressure in our own bodies due to fluids inside is equal to the atmospheric pressure and hence cancels the pressure from outside.