M3C3 Flashcards
Define work done
The work done (or energy transferred) is the product of the force and the distance moved by the force in the direction of the movement.
What is the work done equation?
W = fd W = f cos Ө W = work done (J) f = force (N) d = distance (m)
What is the first law of thermodynamics?
Energy is never created or destroyed. Only transferred into other forms
Define the principle of the conservation of energy
In any closed system, energy cannot be created or destroyed. It can only be transferred from one form to another. The total energy available before any process is always equal to the energy after the conversion has happened
How do you calculate efficiency?
useful energy output
——————————-x100
Total energy output
What is waste energy?
Energy transferred into a form that isn’t deemed useful by humans (no energy is actually wasted)
How do you calculate gravitational potential energy?
GPH = mgh GPH = gravitational potential energy (J) m = mass (kg) g = gravitational field strength (m s^-2) h = height (m)
How do you calculate kinetic energy?
KE = 1/2mv^2 KE = kinetic energy (J) m = mass (kg) v = velocity (m s^-1)
What is the relation between GPE and KE?
GPE = KE mgh = 1/2mv^2
What are the si units for joules?
kg m^2 s^-2
Define power
The rate of work done (how fast energy is used). It’s measured in watts a.k.a. joulse a second (w or j s^-1)
What is one of the equations for power?
P = E/T P = power (w) E = energy/work done (J) T = time (s)
How do you calculate the power of a moving object due to a force?
P = Fv P = power (w or j s^-1) F = force (N) v = velocity (m s^-1)
Define efficiency
The ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in
Why can a device never be 100% efficient? What device is the closest to 100% efficiency?
Energy is always wasted as heat or sound due to friction in most cases. A radiator produces no waste heat as any heat produced isn’t considered waste, so the only waste is the tiny amount so sound produced.
