Untitled Document

For the purpose of the analysis of the vertical jump it is reasonable to consider gravity as the only non-contact force that needs to be identified. Sir Isaac Newton explained gravitational interaction in what is now known as Newton's Law of Gravitation which can be defined as follows:

All particles attract one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

The two factors that are identified by the law as being important in determining gravitational force, are the masses of the objects, and the distance between them. More specifically, the larger the masses and/or the closer the masses, then the larger the gravitational force.

To all intents and purposes the only object with a sufficiently large mass to produce observable changes in the motion of a sports person and/or piece of sports equipment, is the earth. The force which results from interactions with the earth is called GRAVITY. Hence, if a ball is thrown into the air it is seen to be attracted back towards the planet's surface and the same is true of a high jumper, pole vaulter, gymnast, etc.

The gravitational force acting on a particular object is called its WEIGHT and this is clearly dependent on, but distinct from, the MASS of an object. These terms are often used interchangeably but in fact have quite different meanings. Weight refers specifically to the gravitational force acting on the object, whilst mass refers to the amount of matter that actually makes up the object. If someone could do a vertical jump on the earth, and then on the moon, the mass of that person would be the same in both instances. However, the weight of the jumper would be considerably smaller on the moon because the jumper is interacting with a much smaller mass (i.e. the moon), and therefore the gravitational force (weight) acting on the jumper would be smaller. It can be seen that for an athlete whose event involves a significant vertical motion (e.g. high jump) that it is especially advantageous to reduce any excess body mass such as fat and to minimise the mass of kit such as clothes and shoes.

Although the relative sizes of the masses interacting and the distance between the object are variables in determining the magnitude of gravitational force acting on an object, both of these variables are considered to be constant, within the context of the vast majority of everyday event, as any variation in mass or distance would be far to small to make a measurable difference. Therefore a critical factor in explaining the vertical jump movement is to note that the force of gravity acts at constant value in a downward direction during all phases of the jump.

TASK: Look through the recommended text books for the unit (see unit handbook) and note how gravity is represented on diagrams showing gravity acting on sport performers.

TASK: Look at the video and note that the explanation above indicates that gravity is effecting the jumper throughout the movement - not just during the flight phase. Draw stick figures representing the jumper in three different positions (use the video to help guide you). Using the information gained in the reading undertaken in the previous task, sketch a representation of the force of gravity acting on the jumper in three different positions during the verticl jump activity..

Gravity

Factors determining the magnitude of gravitational force

	Gravity

Factors determining the magnitude of gravitational force For the purpose of the analysis of the vertical jump it is reasonable to consider gravity as the only non-contact force that needs to be identified. Sir Isaac Newton explained gravitational interaction in what is now known as Newton's Law of Gravitation which can be defined as follows: All particles attract one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. F = Gravitational force m₁= mass of object one m₂= mass of object two d = distance between objects G = gravitational constant The two factors that are identified by the law as being important in determining gravitational force, are the masses of the objects, and the distance between them. More specifically, the larger the masses and/or the closer the masses, then the larger the gravitational force. To all intents and purposes the only object with a sufficiently large mass to produce observable changes in the motion of a sports person and/or piece of sports equipment, is the earth. The force which results from interactions with the earth is called GRAVITY. Hence, if a ball is thrown into the air it is seen to be attracted back towards the planet's surface and the same is true of a high jumper, pole vaulter, gymnast, etc. The gravitational force acting on a particular object is called its WEIGHT and this is clearly dependent on, but distinct from, the MASS of an object. These terms are often used interchangeably but in fact have quite different meanings. Weight refers specifically to the gravitational force acting on the object, whilst mass refers to the amount of matter that actually makes up the object. If someone could do a vertical jump on the earth, and then on the moon, the mass of that person would be the same in both instances. However, the weight of the jumper would be considerably smaller on the moon because the jumper is interacting with a much smaller mass (i.e. the moon), and therefore the gravitational force (weight) acting on the jumper would be smaller. It can be seen that for an athlete whose event involves a significant vertical motion (e.g. high jump) that it is especially advantageous to reduce any excess body mass such as fat and to minimise the mass of kit such as clothes and shoes. Although the relative sizes of the masses interacting and the distance between the object are variables in determining the magnitude of gravitational force acting on an object, both of these variables are considered to be constant, within the context of the vast majority of everyday event, as any variation in mass or distance would be far to small to make a measurable difference. Therefore a critical factor in explaining the vertical jump movement is to note that the force of gravity acts at constant value in a downward direction during all phases of the jump. TASK: Look through the recommended text books for the unit (see unit handbook) and note how gravity is represented on diagrams showing gravity acting on sport performers. TASK: Look at the video and note that the explanation above indicates that gravity is effecting the jumper throughout the movement - not just during the flight phase. Draw stick figures representing the jumper in three different positions (use the video to help guide you). Using the information gained in the reading undertaken in the previous task, sketch a representation of the force of gravity acting on the jumper in three different positions during the verticl jump activity..

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