Grade 11 Physics

Say them out loud once — a formula you can SAY is a formula you own. The fastest way to pick the right machine is to ask what the story GIVES you — not what it asks for.

The rearranging is the physics — the arithmetic afterward is just bookkeeping.

Acceleration is not about how fast you are going — it is about how fast that is changing.

Two speeds rule the road: physics thinks in m/s, road signs shout in km/h. The bridge between them is exact: an hour is 3600 s and a kilometre is 1000 m, and 3600/1000 = 3.6.

The picture explains the half: distance is the area under the speed line.

From here the paper stops asking one thing at a time. A two-step problem hands the answer of line one to line two as a given — so write each answer down, with its units, before moving on.

Chapter one watched things move. This chapter asks WHY they move: something pushed.

All through kinematics, F = ma sat in the option deck as a trap — nothing had a mass, so it never applied. That diagnosis just flipped.

The ladder is the one you know: pick the formula, rearrange it for what you want, put the numbers in their sockets, and only then compute.

Every kilogram gets charged 9.8 newtons, no exceptions, like a tax. On the Moon the same kilograms would be charged less; the stuff itself never changes.

A coefficient carries none — if your μ ever wears newtons, a rearrangement upstream is lying to you. The subscripts name the state, not a first-and-second: k is kinetic, already sliding, and s is static, still at rest.

Stretch a spring and it answers in proportion: F = kx — F equals k x, where F is the force the spring pulls back with, in newtons, and x is the stretch — how far it has been pulled past its rest length, in metres.

Real objects never feel one force at a time. The push fights friction; the cable fights the weight.

Watch the units in every scenario: a bare N is a force waiting to act, a J is energy banked, and a W — a watt, one joule per second — is energy on the move.

Work is not effort — it is a force times the distance it acts through: W = Fd, W equals F d: the work W in joules, the force F in newtons, the distance d in metres.

The half is honest bookkeeping, but the square is the headline: double the speed and the energy bill QUADRUPLES. Triple it, nine times the bill.

Keep last chapter's warning in force: mg alone is the WEIGHT, a force in newtons. Stop there and you have not reached an energy — the height still has to be paid.

Now watch the m on both sides — it cancels.

Same bill, different clock: a kettle and a campfire can hand the water the same joules, but the kettle does it before the conversation dries up.

No machine hands back every joule: friction, heat and noise all take their cut.

Every wave that will ever appear on your paper is described by four numbers.

Run the free check before any arithmetic: hertz times metres is cycles-per-second times metres-per-cycle — the cycles cancel and m/s falls out, a speed.

Sound has no fixed speed — it borrows one from the air. In dry air the rule is v = 331.3 + 0.606T — the speed v in m/s, and T the air temperature in °C.

A guitar string is pinned at both ends, so the simplest wave it can hold is one bump — HALF a wavelength — between the pins.

Close a pipe at one end and the rules change. The closed end pins the air still — a node — while the open mouth swings free — an antinode.

Your ear spans a trillion-to-one range of intensities, so loudness is scored on a ladder of tens.

The siren that sails past you drops its pitch the instant it passes — that is the Doppler effect, and the sanity rail you must never let go of: approach raises pitch, retreat lowers it.

Four units run this whole chapter, and a water pipe explains them all. Current I, in amperes, is the flow — how much charge streams past per second.

V = IR — read aloud: V equals I R — is the chapter's centre of gravity: pressure equals flow times narrowness, with V the voltage in volts, I the current in amperes and R the resistance in ohms.

Parallel is extra doors: every new branch makes the flow easier, so the total drops BELOW even the smallest branch — always.

The original is P = VI (read aloud: P equals V I) — the push times the flow is the rate of spending energy, measured in watts.

The hydro meter does not count joules — it would need nine digits by breakfast.

Put a current-carrying wire square across a magnetic field and the field pushes on it — the motor effect, and the reason anything electric spins.

Same July sun, same beach: the sand scorches your feet while the water stays cool. Both collected heat all morning — but water is thermally stubborn: it takes a small mountain of energy to move its thermometer one degree.

If your rearrangement's units refuse to cancel, it is wrong — no appeal. (Units that do work out never prove it right.) Two flags for this lesson.

Drop a thermometer in melting ice and watch: heat pours in, and the reading parks at 0 °C until the last crystal is gone.

The named trap is skipping a leg — usually the plateau, because the thermometer stops advertising it. And feel the sizes before computing.

So far we have counted heat in lump sums. But through a window, heat runs as a steady rate — joules every second, which is to say watts, the same watts as any power.

Warm a solid and it grows — every metre of it, by a tiny fixed fraction per degree.