Mechanics Flashcards
Newton’s 2nd law
F= mass * acceleration
Newton’s 1st law
An object at rest will stay at rest and an object at motion will stay in motion unless a net force acts on it
No net force= no acceleration
Newton’s 3rd law
Action reaction pairs
If obj 1 exerts a force on obj 2 then obj 2 exerts a force on obj1 equal in magnitude but in opposite direction
Law of gravitation
Gravitational force= (Gm1m2)/r^2
G= 6.67 x10^-11
Gravitational force is inversely proportional to the square of the distance between centers of objects
Friction
Static
-no relative motion between the surfaces that are in contact
Force= maximum coefficient of static friction* normal force
Kinetic
- when there is motion( sliding)
Force= coefficient of kinetic friction * normal force
Normal force is perpendicular to contact force on obj
Pulley
Device that changes the tension that pulls on the object
If we pull down on the left on the right the pulley will pull up
A pulley system causes a constant tension to exist throughout the entire string
Center of mass
Xcm= (m1x1+m2x2+….)/(m1+m2+…)
Uniform circular motion
An object moving in a circular path where speed is constant( not velocity as direction changes)
Centripetal acceleration: (mass * velocity^2)/ radius
Torque
= Radius * force * sin( theta)
Or
= force * lever arm ( the lever arm is perpendicular to the line of action of the force)
Measure of force’s effectiveness to make an object spin or rotate
Equilibrium
Means zero acceleration
Doesn’t mean zero velocity
Rotational equilibrium means zero net torque
Translational equilibrium means zero net force
Static equilibrium is when force, torque and velocity are zero
Rotational inertia
Inertia- resistance to acceleration
Torque = inertia * rotational acceleration
The farther away mass is from axis of rotation the greater the rotational inertia will be
Work
= force* distance* cos( angle between force and distance)
= - pressure* change in volume
Negative work means work done by the system
Note: expanding gases cool, compressed gases warm
Power
= work/ time
= force * velocity
Kinetic energy
Energy due to motion
=0.5mass* velocity^2
Work energy theorem
Total work done on an object= change in kinetic energy
Potential energy
= mass* gravity* height
Change in potential energy= - work done by gravity
Work done by gravity depends on initial and final heights not on the path object follows making it a conservative force
Friction depends on the path
Total mechanical energy
= kinetic energy + potential energy
When friction isn’t present
Energy initial = energy final
With friction
Energy initial + work done by friction= energy final
Mechanical advantage
= effort distance( with machine)/resistance distance( without)
Tells us how much less force is required by the machine
Machines allow your effort force to decrease
Efficiency
= work output/ energy input
Measures degree to which friction reduced the actual work output
Momentum
Linear momentum= mass* velocity
The momentum of individuals changes not the system
Angular momentum= inertia *angular velocity = lever arm * linear momentum
Inertia is the rotational version of mass
Torque is the rate of change of angular momentum
Impulse
Effect of exerting a force on an object over time
Force* change in time = mass* change in velocity= change in momentum
Collisions
Elastic- kinetic energy and momentum conserved
Inelastic- momentum conserved
Perfectly inelastic- momentum conserved and objects stick together after
Isobaric process
Occurs at constant pressure
Area under PV graph is work
Work = -pressure * change in volume
Isochoric process
Process maintains constant volume
No work is occurring therefore change in energy = heat
Isothermal process
Heat can freely pass between system and surroundings
Temp is constant
No change in energy
Work = -heat
Adiabatic process
No heat is transferred
Change of energy =-work
