Laws of Motion: an interactive mechanics course

Laws of Motion is an interactive physics mechanics course that starts with a cart on a track and ends with projectiles. Its 25 short sections cover speed, velocity and acceleration on velocity-time graphs, forces and free-body diagrams, resultant force, Newton's three laws, mass and weight, friction and air resistance, momentum and collisions, impulse, the equations of motion and projectile motion, with a simulation or practice question in most of them.

Every law comes with something to push: hold a button to apply a force to a cart and watch F = ma draw its velocity-time graph, or crash two trolleys and see momentum shared between them.

What the course covers

Describing motion

Velocity is speed in a direction. On a velocity-time graph, the gradient is the acceleration and the area underneath is the distance travelled, two facts the course comes back to again and again.

Here x is time in seconds and y is velocity in metres per second. The gradient is 10 ÷ 5 = 2 m/s², the acceleration. The area of the triangle under the line up to 5 s is ½ × 5 × 10 = 25 m, the distance travelled.

Forces and Newton's laws

Forces are drawn as arrows on free-body diagrams and combined into one resultant force. Newton's first law says nothing changes its motion without a resultant force; the second says how much it changes; the third says forces come in equal and opposite pairs acting on different objects.

Momentum and the equations of motion

Momentum, mass times velocity, is conserved in collisions, and a force acting over a time changes it by Ft = Δp, which is why crumple zones and airbags work. For constant acceleration, the five SUVAT equations link displacement, velocities, acceleration and time, and the course uses them to solve projectile problems. See our SUVAT equations guide for all five with worked examples.

Try a question from the course

On the graph above the line is straight, so the acceleration is steady: gradient = change in velocity ÷ time = 10 ÷ 5 = 2 m/s². For distance, find the area under the line. It is a triangle, so ½ × base × height = ½ × 5 × 10 = 25 m.

Now read a new velocity-time graph, then press Mark to check your answer in the course.

Who this course is for

• GCSE physics students revising forces, Newton's laws, momentum and velocity-time graphs.
• A-level and other advanced students working on SUVAT, impulse and projectiles in physics or maths mechanics.
• Anyone who wants to understand why seatbelts, parachutes and rockets work the way they do.

What you need to know first

The course page suggests Algebra first: you need to rearrange formulas such as F = ma and work with negative numbers for direction. Projectiles use the equations of motion in two directions, which the course explains step by step.

How long it takes

There are 25 sections and most take a few minutes. Learners without a plan can open two sections of a course a day, in order, so the whole course takes 13 days. A plan removes the daily limit and lets you go straight to any topic, such as momentum or projectiles.

Read next

Physics · MechanicsMomentum calculator: p = mv, impulse and collisionsFind momentum from p = mv, impulse and average force, and the velocities after elastic and perfectly inelastic collisions, with worked examples.