Unit 7 - Work and Energy Flashcards
ENERGY __>
Measure of ability to do ork
Never destroyed
Only ever transformed from one form to another
One Joule is
When one N of force is applied to move an object throguh 1m
What is one calorie
The ammount of energy required to raise 1 kg of water by 1 deg
W=
Fd
Only the component of force that lies __________ to the dispalcement does work
Parallel
Rewrite the equation for Fh
W = Fxcos theta
Kinetic energy is
The energy an object has due to motion which depends on the mass and speed of the object
Ke =
1/2 mv^2
Ke is always
Positive
Due to v^2 being positive or 0
Delta Ke =
W net
Ke is a ________ quantity
scalar
GPE is
Potential an object has to do work as a result of being located at a particualr position in a gravitational feield
GPE =
mgh
What happens if you remove the force holding the object up
GPE converted to Ke of the falling object
Energy (E) =
Power X time
Give the 2 laws of newtons laws of gravitation
F = gm1m2 / r^2
GPE = -Gm1m2 / r
In mechanics what fundamental quantities are conserved
Energy, momentum and angular momentum
Total energy in an isolated system always
Remains the same
What is the equation that shows conservation of energy in an isolated system
Define the terms
Eki + Ugi + Usi = Ekf + Ugf + Usf + Ehf
Ek - kinetic
Ug - GPE
Us - elastic string potential
Eh = heat
i - initial
f - final
summarise the equation stating conservation of energy in an isolated system
Potential/inital energy = final energy
Define thermal energy
Energy contained within a system responsible for its temperature
Heat is the
Flow of thermal energy
Equation for change in thermal energy
Define the terms
Uk . Fn . d
Uk - coefficient of kinetic friction
Fn - normal force
d - distance
What type of friction generates heat, which type doesnt
Force a static friction
Force of kinetic friction
1W =
1 J per second
Power is
The rate at which work is done
3 equations for power
P = delta E / delta t
P = Fv
P = mav
What is stress
force applied per unit of area
What is strain
Extent of streching/compression produced as the material responds to stress is called the strain
Equation of strain
Change in L / Original length
What are the two types of deformation
Elastic and plastic
Elastic
When stress removed it returns to original dimension
REVERSIBLE AND NON PERMANENT
Plastic
Stress is so large that when removed it does not return to its orignal dimensions
IRREVERSIBLE AND PERMANENT
Hookels law is the
Force required to strech an elastic object such as a metal spring is directly proportional to the extension of the spring
F (Hookes Law0 =
- kx
Why must you take care when calculating the length of a spring
substracting the nominal (resting) length
Youngs Modulus –>
Elastic modulus measures the resistance of a material to be elastically deformed
The stiffer the material the ________ the Young’s modulus
Higher
Young’s Modulus =
Stress/Strain
How can you obtain k from Youngs Modulus
K = EA/L
E = youngs modulus A = area L = length
Spring constant when k in serioes
k/2
Spring constant when k in parallel
2k
What is elastic potential energy
EPE is energy tored as a result of applying force to deform an elastic object
EPE =
1/2.k.(delta x)^2
What are the two patterns energy follows
1/2 ab^2
abc
