Grade 12 Physical Sciences (Term 2) Summaries. These summaries are composed using the Platinum textbooks' work with examples and supplementary notes.
A) Topic 4:
* Chapter 6: Work, Energy and Power.
B) Topic 5:
* Chapter 7: The Doppler Effect.
C) Topic 6:
* Chapter 8: R...
Conservation of Mechanical U4: Power:
Energy with Only Scientific Meaning of Power:
Conservative Forces Present:
• Power – scalar – measured in watts.
W E
• Law of conservation of energy: Energy cannot be • P = t or P = t .
created or destroyed, but one form of energy can • Calculating total energy from power: W = P x t
be transformed into an equivalent amount of or W = E x t.
another form.
• In closed system – sum of Ep and Ek remain
constant.
• Net external force acting on system = 0.
• Only conservative forces exist if mechanical energy
Average Power Required to Keep
Sample
conserved.
• Law of conservation of mechanical energy: Total Object Moving Across Rough Surface:
Em (sum of gravitational Ep and Ek) in closed system U3: Conservation
remains constant. • Pav = Fvav.
• Sum of Ep and Ek remains constant during free fall.
of Energy (B) • Power rating on electric machines indicates rate at
• Ep at top = Ek at bottom. which they do work.
U4: Power
Summaries after sample
work done 𝐹∆𝑥 𝑚𝑔 x ℎ
• Power = time taken = 𝑡 = 𝑡
•
Conservation of Energy with Non-
Conservative Forces Present: Mechanical Energy in Absence of
• Don’t conserve mechanical energy. Non-Conservative Forces:
• Energy gained or lost due to dissipative forces.
• Wnet = Wc + Wnc • ΔEk = -ΔEp
• Wnc = ΔEk + ΔEp • Kinetic energy gained = potential energy lost
without conservative forces.
• Sum of Ek and Ep constant.
• Produced through various polymerisation
reactions.
, U1: Definition of Work:
• Work done on object when
force is exerted on the object,
and it moves in direction of
force. Net Work Done on Object:
• W = F x ∆𝑥 x cos θ
• Work – scalar. • When more than 1 force acts on an object – W done is
• SI unit for work – Newton-metre the sum of all the W done by each force in direction of
called the joule. motion.
U1: Definition
of Work
Positive and Negative Work:
• Positive work – F in direction of motion – increasing
Instances in Which Work is or isn’t Done: system’s energy.
• Negative work – F in opposite direction to motion –
• Work only being done when force acts on object and decreasing system’s energy.
object moves in direction of force. • Forces exerted at right-angle to motion or no
• If force exerted at angle to direction of motion – only the motion – no W done.
component of force parallel to direction of motion does • Forces exerted at angle to direction of motion –
work. only F parallel to direction of motion does work.
• Work done in lifting objects: W = mg x h
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