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2023 Tahsili Physics, energy and machines
System Types
open system |
can gain and lose mass and energy |
closed system |
a system that does not gain nor lose mass |
Isolated system |
a sytem that does not exchange mass nor energy |
Momentum and Impulse
impulse (I) |
I or ΔP = FΔt |
impulse unit |
N.s |
Location on a graph |
under the Force - Time curve |
Momentum |
P = mv |
Law of Conservation Of Momentum |
m1v1 + m2v2 = (m1+m2)v |
in any closed or isolated system, the momentum is conserved |
impulse is the change in momentum, so I = ΔP |
Kinetic Energy
KE Formula |
KE = (1/2)mv2 |
work-energy theorem |
work is equal to the change in KE ( W = KEf - KEi ) |
Potential Energy
Gravitational Potential Energy |
energy stored as a result of the gravitational attraction of the earth on the object |
Formula |
PE = mgh |
Elastic Potential Energy |
the energy stored in elastic materials as a result of their stretching or compressing |
Machines
Simple Machine |
a machine that makes work easier by changing the value of force or its direction |
compound machine |
a device that uses multiple simple machines |
Mechanical advantage |
Fr / Fe (resistance force / effort force) |
Ideal Mechanical Advantage |
de / dr (effort displacement / resistance displacement) |
Compound Mechanical Advantage |
the product of the MA of its simple machine components |
Efficiency |
(W output / W input) x 100% or (MA / IMA) x 100% |
Types of simple machines |
pulley - lever - wedge - incline plane - screw |
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Collision Types
Inelastic collision |
the kinetic energy after the collision is less than it originally was |
elastic collision |
the kinetic energy remains the same after the collision |
super elastic collision |
the kinetic energy increases after the collision |
kinetic energy decreases when the objects stick together |
Work
Work |
the translation of energy in mechanical ways |
Work Formula |
Fdcos(θ) |
Work Unit |
J |
Location on graph |
under the force - displacement curve |
Work done by Friction |
-fk x d |
Work done by Gravity |
mgd |
Work = 0 |
when the force is perpendicular to the displacement (90 degrees) |
W is positive |
if the work is done on the system |
W is negative |
if the work is done by the system |
Mechanical Energy
mechanical energy |
the sum of the potential and kinetic energies |
Power
Power |
P = W/t |
Power Unit |
Watt = kg.m2/s3 |
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