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Biomechanics Test Two
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Flashcards
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Terms in this set (39)
Inertia
The natural tendency of an object to remain at rest or in motion at a constant speed.
Variable(s) that describe linear and angular inertia
Mass; mass and distance of mass from the axis of rotation
Linear version of Newton's Law of Inertia:
A body at rest stays at rest, a body in motion stays in motion along a straight line unless acted upon by a net force.
Angular version of Newton's Law of Inertia:
A body at rest stays at rest, a rotaing body stays in rotation unless acted upon by a net torque.
Linear version of Newton's Law of Acceleration:
The acceleration experienced by a body' is directly proportional to the net force and invesely proportional to the mass and it occurs in the direction of the force
Angular version of Newton's Law of Acceleration:
The angular acceleration expeirenced by a body is directly proportional to the net torque and inversely proportional to the moment of inertia and it occurs in the direction of the net torque
Work-Energy Priniciple states:
The change in energy is equal to the work done.
Law of Conservation of Energy states:
The total energy is constant during in-the-air motion.
Elastic collision
The objects bounce off each other and have their own momentums.
Inelastic collision
The objects stick together and have a new combined momentum
Steps in computing torque about some axis:
1) Find axis of rotation
2) Determine the sign of the torque (CW or CCW spin caused by torque)
3) Find the length of the lever arm (perpendicular distance)
Does a positive force always create positive torque?
No, hence the CW and CCW rotations
Moment of Inertia is
An object's resistance to angular change.
How is moment of inertia calculated:
By ∑ the product of the mass × the ² distance to the axis of rotation. I=∑md²
Impulse is defined as
The product of the average force and the time interval (∆t) during which the force acts.
How can you generate or absorb angular momentum?
By applying torque, or angular impulse.
Law of Conservation of Angular Momentum:
Angular momentum can be increased or decreased over time. When an object or performer is in the air, it is not possible to apply torque since there is nothing to push or pull against, and as a result, angular momentum is constant in the air.
While in the air a diver goes from tuck position to a layout position to prepare to enter the water. Describe the change in each of these variables (moment of inertia, angular velocity, angular momentum).
Increase in moment of inertia, decreased in angular velocity, angular momentum is conserved.
Kinetics:
The study of forces and the motion they cause.
Mass is
A quantitative measure of the amount of inertia an object has; a SCALAR-it only has magnitude
Law of Inertia:
A body at rest stays at rest, a body in motion stats in motion, also called LAW of MOTION, as it refers to constant velocity and zero velocity
Law of Acceleration:
The acceleration experienced by a body is directly proportional to the net force and inversely proportional to its mass and it occurs in the direction of the force. ∑F=ma
Law of Reaction:
For every action there is a opposite and equal reaction.
Reaction force:
Accelerates your center of mass
Free-body diagram (FBD)
Is a picture that represents an object or performer and all of the forces acting on the object or performer.
Principle of Conservation of Linear Momentum
The total linear momentum of a system of objects is constant if the net external force acting on the system is zero.
Impulse
The average force and the time interval ∆t during which the force acts. Impulse ( J ), is a vector quantity
Impulse is defined as
Average force X time or the area under the force-time curve
To measure impulse:
1) Measure force x time, 2) multiply mass X ∆ in velocity.
Braking impulse:
Will decrease the velocity of the center of mass.
Propulsion impulse:
Impulse where the direction of the impulse is the same as the direction of motion.
Relationship between Force and Acceleration:
Remember form Newton's 2nd Law of Motion that acceleration is directly related to force and that acceleration occurs in the direction of the net force. The shape of the acceleration curve is ALWAYS the same as the shape of the force curve. If you divide the force curve by mass then you have an acceleration curve.
Work:
The magnitude of force X distance
The work-energy principle applies:
Whenever you are in contact with the ground or some external object. As long as you can apply a force over some distance you can change the energy of an object or performer.
Steps in Computing Torque:
1) Take the magnitude of the Force (ignore + or -).
2) Find the Line of Action of the Force
3) Determine the Lever Arm (I), or moment arm which is the Shortest distance from the Line of Action of the Force to the Point of Torque Calculation.
4) Determine the Direction of Rotation th FOrce will cause about the Point of Torque Calculation. T=|F| × l
The work done by a "variable source" is
equal to the area under the force - "distance" graph.
Potential energy
Sometimes referred to as gravitational potential energy, si the energy a body possesses due to its position. Units are J. Potential energy is SCALAR; PE=mgh
Total mechanical energy a body possesses is
simply the sum of kinetic energy and potential energy.
At the peak of a flight all of the total energy is
equal to potential energy
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