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© Tony Fagelman 2006

Club Coach

Mechanics


Take-Off

• Time is a major factor• Take-off is the most

important part of any skill

• Without a good take-off, the skill cannot be performed correctly


Flight

• This is 2nd part of any movement using the trampoline

• The flight requires control and phasing


Landing

• Safety is a major factor

• Performer must be in control

• Preparation for next skill


Newton’s Laws of Motion

• 1st Law :– A body will continue in its uniform state of motion or

rest unless acted on by an external force.• 2nd Law:

– The rate of change of momentum is proportional to the force causing it and the change takes place in the direction in which the force acts.force = mass x acceleration

– if mass is constant, acceleration is proportional to the applied force

• 3rd Law:– For every action there is an equal and opposite

reaction


Centre of Mass

• The point though which the line of force of “attraction to the earth” takes place.

Centre of Mass


Forces

• Push & Pull– A force is needed to:

• Start a motion• Change the rate of motion• Change the direction of motion• Cause motion to stop


TORQUE

• The Rotational push or pull• Caused by a FORCE

• Eccentric or Off-Centre Force also called Torque– This will always create rotation– A torque whose line of action does not

pass through the centre of mass of the body on which it acts


Displacement of COM

• What happens when we displace the Centre of Mass outside the body?

Centre

of

Mass


Linear Movement

• Movement in a straight line• Remember Newtons’ 1st

law– A body will carry on unless

acted on • A trampolinist will bounce

upwards until gravity pulls them back down again


Angular Movement

• An off-centre force acting around the Centre of Mass will create angular movement (Somersault rotation) (Remember displacement of COM)

• Rotation around an axis• Somersaulting demonstrates

both Linear Movement and Angular Movement


Axis of rotation

• somersault axis• twisting axis• side somersault axis

Any rotation can be described using the 3 axis.


Inertia

• The resistance of a body to change • Inertia is measured by Mass

• Or Not… as the case may be


Momentum

• Is the amount of Linear Movement “energy” in a body as it moves

• It is the “quantity” of motion– Velocity x Mass


Speed

• Is the rate of movement of the Centre of Mass


Conservation of Linear Momentum

• Conservation & Creation– Whatever you put into a closed system is

what you have.• Remember Newton’s 1st Law• Can a performer do anything to help themselves to

safety if they do not have sufficient somersault rotation?


Changing Linear Momentum

• All changes in Linear momentum are caused by external forces.

• The changes are determined by the size and direction of the force


Projectile Motion

• when a performer is in flight he/she is a projectile

• the only force acting on them is the force of gravity

• the flight path is predetermined and will not change once in flight.

• the CoM will follow a parabolic flight path


Moment of Inertia

• The measure of the body’s reluctance to start rotating (or change direction) around an axis


Angular Speed

• The rate of rotation around an axis

• To control angular speed in flight (by changing the moment of inertia), the body can change shape


Angular Momentum

• The amount of rotational energy in a body as it rotates around an axis


Changing Angular Momentum

• These are caused by external torques.

• The changes are determined by the size and direction of the torque


Conservation of Angular Momentum

• Angular momentum will remain the same until changed by an external torque– Tucking when

somersaulting– Straightening when

somersaulting


Mechanics of somersaulting

• Creation of a somersault

• Angular movement is caused by TORQUE

• Torque = Force x Perpendicular distance from axis of rotation


Early Twist

• Twist is initiated from the bed

Arms are set whilst in contact with the bed. Movement is initiated

Trampolinist has left the bed

Arms are brought together to allow twist to continue


Late Twist

• The Twist is initiated in the air– There are a number of

theories given to this action.


Tilt Twist

• By moving the body outside the line, twist can be initiated

• The greater the tilt, the greater the twist


Asymmetrical arm twisting

• By moving the arms asymmetrically, twist can be generated

• The greater the arm movement, the larger the twist

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