Unit 1.4 Energy concepts Flashcards
Define work.
It is done when a force moves its point of application.
Define energy.
The energy of a body or system is the amount of work it can do.
Give the units for work.
Joule (J)
What type of quantity is energy?
Scalar quantity
What is kinetic energy?
Energy due to motion.
State the formula work done.
Work done = Force x Distance moved in the direction of the force
State the formula for work done in symbols.
W = Fx
Give the units for the symbol “W”, in work done formula.
(J) - Joules
Give the units for the symbol “F”, in work done formula.
(N) - Newtons
Give the units for the symbol “x”, in work done formula.
(m) - metres
State another way of saying work done.
Energy transfer
Explain energy.
Quantity of energy transferred is equal to the work done by force.
State 2 other formulas for work done.
(1) Work done = Force x Component of displacement in the direction of the force
(2) Work done = Component of force in the direction of displacement x Displacement
State the 2nd formula of work done in symbols.
W = Fxcosθ
Explain in terms of energy, if θ = 90°
No work is done; no energy is transferred.
Explain in terms of energy, if θ > 90°
The work is negative and energy is transferred from the object.
State the principle of conservation of energy.
The total energy of an isolated system is constant though it can be transferred within the system.
State the principle of conservation of energy in symbols.
ΔE - FvΔt - FvΔt = 0
What does the principle of conservation of energy mean?
Work done = energy transfer
Define kinetic energy (KE or Eₖ).
The energy possessed by a body by virtue of its motion.
State the formula for KE.
KE = 1/2 mv²
Explain the formula for KE.
It is the KE of a body of mass “m” travelling with velocity “v”.
Define gravitational potential energy (GPE or PE or Eₚ).
The energy possessed by an object by virtue of its position.
State the formula for GPE.
ΔEₚ = mgΔh
Define elastic potential energy (Eₚ).
The energy stored in a body by virtue of its deformation.
Give examples of elastic objects.
- Rubber bands
- Springs
- Rulers
Describe elastic objects.
Elastic objects which are deformed are able to do work on other objects when they return to their normal shape.
Give 3 ways for an object to be deformed.
- Stretched
- Compressed
- Bent
What does the extent of deformation depend upon?
The applied force
State the formula for Hooke’s law.
F = kx
Define “k” in the formula for Hooke’s law.
Spring constant, k
Define “F” in the formula for Hooke’s law.
Applied force, F
Define “x” in the formula for Hooke’s law.
The deformation (e.g. stretch), x
State the formula for elastic potential (Eₚ).
Eₚ = 1/2 kx²
Define power.
The work done per unit time or the energy transferred per unit time.
Give the SI units and the normal units for power.
(W) - watt
SI Units - J s⁻¹
State the formula for power.
Power = energy transferred/ time
State the formula for power in symbols.
P = E / t
State the formula for energy transferred.
Energy = Power x time
State the 2nd formula for power.
Power = work done / time
State the 2nd formula for power in symbols.
P = W / t
State the 3rd formula for power.
P = Fvcosθ
What is the increase in GPE equal to?
The work done against the force of gravity.
What is the increase in EPE equal to?
The work done against the tension within the object when we stretch it.
Define efficiency.
It is the fraction of the energy input which is transferred usefully by the system.
Define efficiency as a formula.
Efficiency = ( useful energy transfer / total energy input ) x 100%
