NCERT CLASS IX - Science Textbook
Chapter 9 - Force and Laws of Motion
A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team.
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Foot ball is kicked with an impact (contact) force during a short duration of time. There is an impulse given to the ball, which is force * time duration.
The ball gains momentum (speed and direction), floats in air, and/or rolls on the ground. There is a buoyancy force due to air on the ball acting upwards and there is a gravitational attraction (weight) on the ball acting downwards. The ball traces a parabolic path in air. When the ball rolls on the ground or slides on the ground, there is a friction force between the ground and the ball.
When the ball is stopped by the team mate, the teammate applies a ret_arding force during a short duration of time. There is an impulse in the opposite direction reducing the momentum of the ball.
When the ball is collected by the goal keeper, the ball slows down due to soft handling of the ball, and due to negative impulse given by the goal keeper.
When the ball is stopped by a footballer, or the goal keeper, there is a force acting on the person by the ball. This force is countered by the force in the opposite direction by the friction between the ground and the person, and the reaction force from the ground.
Before a person kicks the foot ball, the footballer pushes the ground backwards. There is a force acting on the footballer in the forward direction. This force is transferred to the ball. The footballer remains stationary due to the force exerted by the ball on the footballer in the opposite direction.
If the football on the ground is kicked in the direction passing through the center of the ball, then it only goes in a translatory motion, in a straight line or a parabola in air. If the direction of force is not passing through the center of the ball, then the ball spins in air or on ground due to a torque or the moment of force.
The ball gains momentum (speed and direction), floats in air, and/or rolls on the ground. There is a buoyancy force due to air on the ball acting upwards and there is a gravitational attraction (weight) on the ball acting downwards. The ball traces a parabolic path in air. When the ball rolls on the ground or slides on the ground, there is a friction force between the ground and the ball.
When the ball is stopped by the team mate, the teammate applies a ret_arding force during a short duration of time. There is an impulse in the opposite direction reducing the momentum of the ball.
When the ball is collected by the goal keeper, the ball slows down due to soft handling of the ball, and due to negative impulse given by the goal keeper.
When the ball is stopped by a footballer, or the goal keeper, there is a force acting on the person by the ball. This force is countered by the force in the opposite direction by the friction between the ground and the person, and the reaction force from the ground.
Before a person kicks the foot ball, the footballer pushes the ground backwards. There is a force acting on the footballer in the forward direction. This force is transferred to the ball. The footballer remains stationary due to the force exerted by the ball on the footballer in the opposite direction.
If the football on the ground is kicked in the direction passing through the center of the ball, then it only goes in a translatory motion, in a straight line or a parabola in air. If the direction of force is not passing through the center of the ball, then the ball spins in air or on ground due to a torque or the moment of force.
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Explanation:
The velocity of football changes four times. First, when a football player kicks to another player, second when that player kicks the football to the goalkeeper. Third when the goalkeeper stops the football. Fourth when the goalkeeper kicks the football towards a player of his own team.
Agent supplying the force
First case – First player
Second case – Second player
Third case – Goalkeeper
Fourth case – Goalkeeper
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