Motion and forces for high-school physics: study cards over three tiers, the tricky ones, a practice quiz at three levels — Foundation, On-Level, and Challenge — and a lab where you graph a ball thrown straight up, label the free-body diagram of a box on a ramp, put a Newton's-law argument in order, and argue from cart data whether momentum was conserved when the numbers come up 5% short. Work here, or print it and use a pencil — both count.
Two identical balls at the same height. One is dropped; the other is fired sideways at the same instant.
Split every projectile into horizontal and vertical and solve them separately. Horizontal speed does NOT change the fall time — only the height does. Draw it, split it, sum it.
What people get wrong
⚠️People often think…
On a ramp, the normal force equals mg.
Only on flat ground. On an incline the surface only has to hold up the component pressing into it: N = mg cos θ. And since friction follows the normal force, getting N wrong makes the friction wrong too.
On a ramp, N = mg cos θ.
⚠️People often think…
Something spinning in a circle feels an outward force throwing it out.
Every real force on it points IN — the string, the road, gravity. Cut the string and it flies off in a straight LINE, not outward along the radius. What feels like an outward push is just your own inertia.
The force points in. Inertia does the rest.
⚠️People often think…
Astronauts float because there is no gravity in orbit.
Gravity up there is nearly as strong as on the ground — that is exactly what holds them in orbit. They float because they are in free FALL, moving sideways fast enough that the ground curves away as fast as they drop.
Orbit is falling and missing.
⚠️People often think…
Balanced forces and action–reaction pairs are two names for the same thing.
Balanced forces act on ONE object and cancel there. An action–reaction pair acts on TWO different objects and never cancels on either. A free-body diagram covers one object at a time — which is exactly why it sorts this out.
One object balances. Two objects pair.
Draw it, split it, sum it
1Watch one
A ball rolls off a table at 3 m/s. Another is dropped from the same table. Which lands first?
Split the problem. Vertical and horizontal are independent.
Vertically, both start with zero downward speed and feel the same g.
The height is the same, so the fall time is the same.
They land together. The rolling one just lands further away. ✓
2Do one with me
Fill in what each force does.
Horizontal speed changes the fall time by this much:
On a ramp the normal force is mg times
In a circle, the net force points
💬One sentence, then you move on
Why does horizontal speed not change the fall time?
3Try one
Cut the string on a ball swung in a circle. Which path does it take?
I want a hint first
An object with no net force keeps doing exactly what it was doing, in the direction it was already going.
💬Last one — then you're done here
Why are astronauts weightless if gravity is still strong up there?
Where this goes
Where this lives
Taking a curve too fast, why a truck needs a longer runaway ramp, why a satellite dish points where it does, why a car on ice keeps going straight.
What this feeds
Next unit is energy, waves and electricity — the other half of physics.
Name one time you felt your own inertia in a vehicle.
One card at a time — tap “Show me” to check yourself, then Next. Start at Foundation; when those feel easy, climb.
Helpful Hints
🪜 Motion and forces — the ladder
Position, velocity, acceleration — each the rate of change of the last → three kinematic equations cover constant acceleration; free fall is g = 9.8 m/s² → vectors split into x and y, and a projectile is two independent problems → a free-body diagram shows every force; the net force divided by mass is the acceleration → friction is μN, static holds and kinetic slides → circular motion needs mv²/r toward the center, and gravity, Gm₁m₂/r², is that force for every orbit → momentum p = mv is conserved axis by axis in every collision, and impulse FΔt is how it changes.
Describe it, then explain it: kinematics, then Newton.
🤝 The whole idea
Every problem here is the same three moves: draw the situation, split into axes, apply ΣF = ma or conserve momentum on each axis. The hard part is never the algebra; it is the diagram.
Draw it. Split it. Sum it.
⚠️ Tricky ones
Horizontal speed does NOT change fall time. Height does.
On a ramp the normal force is mg cos θ, NOT mg. Friction follows the normal force.
Balanced forces act on ONE object. Action–reaction pairs act on TWO. They are not the same thing.
There is no outward “centrifugal” force on the object. The force points IN; the object’s inertia does the rest.
Weightless is not gravity-less. Orbit is falling sideways fast enough to miss.
Momentum is conserved in EVERY collision. Kinetic energy only in elastic ones.
Momentum is a vector: conserve x and y separately, then recombine.
📐 The forces on a free-body diagram — the chart
Force
Direction
Size
When it appears
gravity (weight)
straight down
mg
always, near a planet
normal
perpendicular to the surface
whatever balances the push into the surface (mg cos θ on a ramp)
touching a surface
friction
along the surface, against sliding
up to μₛN (static); μₖN (kinetic)
touching a rough surface
tension
along the rope, away from the object
solve for it
a rope, cable or chain
applied
whichever way the push or pull points
given
a hand, an engine, a spring
centripetal (not a new force)
toward the center
mv²/r
the NET force that some real force must supply in circular motion
Draw every row that applies; “centripetal” is a requirement, not an arrow.
🎯 How the test will ask
“A ball rolls off a table 1.25 m high at 4 m/s. Where does it land?” (0.5 s, 2.0 m).
A box on a ramp with μ given — “draw the free-body diagram and find the acceleration.”
“Identify the action–reaction pair for the normal force on a book.”
“Find the maximum speed a car can round a curve of radius r with coefficient μ.”
Two carts collide and stick — “find the final velocity; is KE conserved?”
“Explain, using impulse, why a padded landing hurts less.”
✅ Can you…
Pick the right kinematic equation and read slope and area off a graph?
Solve a projectile by keeping the axes separate?
Draw a complete free-body diagram, including on a ramp?
Tell a balanced pair from a third-law pair?
Find the force to round a curve and the speed at which friction runs out?
Conserve momentum in two dimensions and account for the lost KE?
Pick your level
Look back at anything you missed — the hint that appeared is exactly what to reread tonight.
How sure did you feel?
Lab
Work like a scientist: label the diagrams, turn the table into a graph, then write a claim with evidence and reasoning. Every lab checks itself on the spot, and hints are free.
Your practice never leaves this device. There is no account and no sign-in. Your work is saved in this browser only, and you can erase it whenever you want.
Your practice record — saved on this device
This is your record of the module on screen — it stays here and goes nowhere. Independent means you got it right on the first tap; supported means you got it after the explain-and-retry, or marked ‘I had it’ on a revealed answer. Both count, and neither is a grade. If your teacher asks, copy the row or show them this screen.
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