Forces act on every object and here we consider both cases of equilibrium and the resultant motion.

Force, Mass, Acceleration and Newton's Second Law

You should remember most of this from GCSE Physics, but it's good to refresh your knowledge. F=ma is a special case of Newton's Second Law provided you have a constant mass and a uniform acceleration, and it used throughout this subject to calculate how objects change their motion when a net force is applied.

Mass and Weight

Mass and weight are words used all the time in everyday life - often in the 'wrong' way. 

Centre of Mass and Gravity

How do you measure the centre of mass (or centre of gravity) of an object? And are they always in the same place? Find out more in this video.

Free Body Diagrams and Objects on an Inclined Plane

Diagrams are really important to allow you to visualise the various forces acting on an object. We can use this technique to see what happens when an object is at rest on a slope - a really tricky example.

Drag, Air Resistance and Water Resistance 

As an object moves through a fluid (gas or liquid) it collides with particles which impedes its motion. This is known as drag and here I show you which factors affect it the most.

Terminal Velocity

When an object falls and is subject to a drag force then it will end up falling at a constant velocity. Here I explore this subject in more detail.

The Principle of Moments

Apply a force at a distance and you have a turning effect which we call a moment. I show you how to calculate the moment when a force acts at an angle. Finally, for an object in rotational equilibrium the sum of the anti-clockwise and clockwise moments is zero which is the principle of moments.

Torque of a Couple

If you have two equally sized forces that acts towards each other but are offset then you have a resulting moment but no resulting force. Because there are two forces we call this the torque of a couple.


Density is a measure of the amount of 'stuff' per unit volume. But what happens when you add salt to an egg in water?


Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

Pressure in Liquids and Fluids

As you dive deeper into the sea the pressure you experience becomes greater. Have a look at this video where I explain why.

Upthrust and Archimedes' Principle

Why do objects float? Here I show you why the upthrust is equal to the weight of the fluid displaced.

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