Exam 3 Flashcards
Newton’s First Law
A body will remain at rest or continue to move with a constant speed in a straight line unless acted upon by an outside force.
Outside forces
Any forces that are external and will change the momentum of a system.
A push or pull by one body on another
Force
Newton’s Second Law
Acceleration is caused by a net force and is proportional to the magnitude of the force, and in the direction of the force.
A force that is causing a body to speed up
Propulsive force
This force is positive in the positive direction and negative in the negative direction.
Propulsive force
A force that is causing a body to slow down.
Braking force
This force is negative in the positive direction and positive in the negative direction.
Braking force
The force on a body due to gravity
Weight
Formula for weight
Weight = (mass)(acceleration of gravity)
Acceleration of gravity
-9.81 m/s^2
How many newtons in a pound?
1 lb. = 4.45 N
How many newtons in a kilogram-meter/second^2
1 N = 1 kgm/s^2
The cause of acceleration
A net (effective) force
Newton’s Third Law
For every force, there is an equal and opposite reaction force.
The force created when two bodies are touching each other.
Contact force
A force of equal in magnitude and opposite in direction of the initial force.
Reaction force
The equal and opposite force that the ground applies back on a person.
Ground reaction force
This opposes motion between two objects in contact.
Friction
Will always be parallel to the contact area.
Friction
Caused by irregularities in the surfaces between two objects.
Friction
Are always acting in different bodies.
The force and reaction forces.
Formula for Newton’s Second Law
Force = (mass)(acceleration)
The product of average force and the time that the force is applied.
Impulse
Equal to the change in momentum
Impulse
How can a force be effective?
To be effective, a force has to be applied over time (or over a distance).
Formula for impulse
Impulse = (force)(time)
RFD
Rate of force development
RFF
Rate of force fatigue
Is impulse equal to momentum?
Yes
Variables to decrease the need for an effective force
Mass
Initial velocity
Final velocity
Time
The amount of impulse that can be generated relative to body mass
Relative impulse
Angular equivalent of Newton’s First Law.
Angular momentum of a system will not change unless acted upon by an outside force.
The turning effect of a force
Torque
Synonymous with torque
Moment of force (moment)
Formula for torque
(Lever arm)(perpendicular force) = torque
Distance from the axis of rotation to the point of force application
Lever arm
Perpendicular distance from the force vector to the axis of rotation
Moment arm
Formula for moment arm
(Force)(perpendicular distance) = torque
A torque that is increasing the speed of rotation
Propulsive torque
A torque that is decreasing the speed of rotation
Braking torque
This torque will not always be in the same direction as the motion of the body.
Muscular torque
The effect of the net sum of all torque vectors acting on a body
Net (effective) torque
A rigid body that is used in conjunction with a pivot point to multiply the force or speed applied to another body
Lever
Four components of a lever
Pivot point (fulcrum)
Rigid body
2 forces
How do levers work as force multipliers?
The force further away has a mechanical advantage over a closer force. Thus it creates greater torque for the same amount of force.
The four functions of a lever
- Balance two or more forces.
- Change the direction of the applied force.
- Favor speed and range of motion.
- Favor force production.
Components of levers
- Applied (motive) force
- Force moment arm
- Axis of rotation
- Resistance force
- Resistance moment arm
The components used to classify a lever
Force (F)
Axis of rotation (A)
Resistance (R)
Arrangement of a first class lever
F-A-R or R-A-F
The most versatile lever: can be manipulated to serve all four functions.
First class lever
Examples of first class levers in the body
Neck extension
Elbow extension
Arrangement of a second class lever
A-R-F
Examples of second class levers in the body
Push-up
Toe raise
Arrangement of a third class lever
A-F-R
Examples of third class levers in the body
Elbow flexion
Each component of a force has the potential to produce both a
Linear and angular acceleration
Two forces equal in magnitude, opposite in direction, and in the same plane.
Force couple
Produced pure rotation with no translation
Force couple
Examples of a force couple in the body
Pelvic girdle rotation
Maximizing angular velocity would
Improve performance
Decreasing the average torque would
Minimize injury risk
A resistance that increases with the amount of force or torque applied to it.
Accommodating resistance
Maintains constant angular velocity no matter the torque
Isokinetic dynamometers
Examples accommodating resistance
Flywheels
Isokinetic dynamometers
When linear and angular accelerations are zero, and the sum of the external forces and torques are zero
Static equilibrium
How many forces and torques involved in holding an object
11 forces
10 torques
The state of matter that makes things change or has the potential to make things change
Energy
Types of energy
Nuclear Chemical Electromagnetic Acoustic Mechanical
The state that characterizes a body or system
Energy
The energy that a body has due to motion
Kinetic energy
The energy a body has that has the potential to change something
Potential energy
The energy a body has due to its deformation
Strain potential energy
The potential energy a body has due to its position
Gravitational potential energy
Conservation of energy
Energy can neither be created nor destroyed; it can only be transformed from one state into another or transferred into or out of s system.
Formula for work
Work = (force)(distance)
The process of changing the amount of energy in a system
Work
Energy is entering the system
Positive work
Energy is leaving the system
Negative work
Torque does the work, not force. Potential energy would still increase
Angular work
Lower energy requirement for the same amount of work
More economical movement
The amount of energy required to perform a certain amount of work
Economy
Acts like an inverted pendulum
Walking
Modeled as mass on top of a spring
Running
The time rate of doing work
Power
How much force can be produced while moving quickly
Power
Formula for momentum
Momentum = (mass)(velocity)
A collision where two objects bounce off each other without deformation of loss of heat
Elastic collision
A collision where two objects stick together after they collide
Inelastic collision
Energy conserved in elastic collision
Kinetic energy
Energy conserved in inelastic collision
Not kinetic energy
The object’s relative velocity remains the same in
Perfect elastic collisions
The portion of a body’s mass that is involved with a collision
Effective mass
Formula for power
Power = work/time
Unit for work
Joules
Formula for kinetic energy
Kinetic energy = 1/2(mass)(velocity^2)
Formula for potential energy
Potential energ = (mass)(gravity)(height)
