Linear Kinetics Flashcards
Linear Kinetic
Study of the forces associated with linear motion
Law of Gravitation
All bodies are attracted to one another with a force:
- Proportional to the product of their masses
- Inversely proportional to the distance between them
Newton’s 1st Law
- Law of Inertia
- An object in motion or at rest will remain so unless acted on by a sufficient external force
Newton’s 2nd Law
- Law of acceleration
- A force applied to a body causes an acceleration of that body
- F = ma
Newton’s 3rd Law
- Law of Reaction
- For every action, there is an equal and opposite reaction
Normal Reaction Force
Force acting perpendicular to 2 surfaces in contact
Orthogonal
2 surfaces are perpendicular to each other
Friction
A force that acts at the area of contact between 2 surfaces in the opposite direction of motion
Static Friction
- Force acting over the area of contact between 2 surfaces
- Increases as the opposing force increases, but motion does not occur
Maximum Static Friction
- Max amount of friction that can occur between 2 stationary surfaces in contact
Kinetic Friction
- Constant magnitude friction generated between 2 surfaces in contact during motion
- Always less than max static friction
Coefficient of Friction
- μ (mu)
- Unitless # indicating the relative ease of sliding or the amount of mechanical and molecular interaction between 2 surfaces in contact
Static Friction Equation
F(s) = μ(s)R
Maximum Static Friction Equation
F(m) = μ(m)R
Kinetic Friction Equation
F(k) = μ(k)R
Rolling Friction
- Friction between a rolling object and the surface on which it rolls
- Lower than sliding friction
Linear Momentum
- The quantity of motion a moving body possesses
- M = mv
Principle of Conservation of Momentum
In the absence of external forces, the total momentum of a given system remains constant
Impulse
- Product of force and the time over which the force acts
- Change in momentum
- Impulse = Ft
Impact/Collision
A collision between 2 bodies characterized by the exchange of a large force during a small time interval
Perfectly Elastic Collision
- Collision during which the velocity of the system is conserved
- Ball will bounce to the drop height
Perfectly Plastic Collision
- Impact resulting in the total loss of system velocity
- Object will not bounce at all
Coefficient of Restitution
- Unitless number that serves as an index of elasticity for colliding bodies
- 0 = plastic
- 1 = elastic
Coefficient of Restitution Equations
-e = (v1 - v2)/(u1 - u2)
- v = relative velocity after impact
- u = relative velocity before impact
e^2 = h(b)/h(d)
- h(b) = bounce height
- h(d) = drop height
Law of Impact
When 2 bodies undergo a direct collision, the difference in their velocities after impact is proportional to the difference in their velocities before impact
Direct Impact
Impact which is either “head on” or at right angles to the surface
Oblique Impact
Impact which occurs at angles that are not perpendicular
Work
- W = Fd
- 1 J = 1 Nm
Positive Work
Net muscle torque and angular joint motion are in the same direction (concentric)
Negative Work
Torque and motion are in the opposite direction (eccentric)
Power
- Rate of work production
- P = W/t
- P = Fv
- 1 W = 1 J/s
Energy
The capacity to do mechanical work
Kinetic Energy
- Energy of motion
- KE = 1/2mv^2
Potential Energy
- Energy of position
- PE = wt x h
- PE = mgh
- 1 J = 1 Nm
Law of Conservation of Mechanical Energy
- When gravity is the only external force, a body’s mechanical energy will remain constant
- C (constant) = PE + KE + TE
Strain/Elastic Energy
- A form of potential energy
- Capacity to do work by virtue of a deformed body’s return to its original shape
- SE = 1/2kx^2
