# Forces

#### Chapter 3 - Forces

In the GCE A Levels, we must understand that the weight of an object is calculated as the product of its mass and the acceleration due to gravity. The weight always acts downwards and from the centre of gravity of the object.

In the GCE A Levels, tension is a common force we must deal with. This is the force we get in a string or rod when it is taut. Here we understand that tension must always act away from the object we are studying, and if we are looking at the same string or rod, the tension must be uniform throughout.

In the GCE A Levels, we have to recognise that objects that are touching a surface, will experience a normal contact force from that surface. We will understand some of the key features of the normal contact force, including what it means, and also how it should be represented.

In the GCE A Levels, we understand friction has a force that opposes motion on surfaces, or the tendency for that object to move. No quantitative formulae are required for friction, but we will briefly introduce a simple formula for both static and dynamic friction, and discuss the differences between these two types of friction.
In the GCE A Levels, we must appreciate that objects moving in fluid mediums will experience drag force. This video will explore the various properties of drag, including a simple quantitative way to calculate it.
Hooke’s Law describes the relationship between the restoring force on an elastic object and its extension. In the GCE A Levels, we typically use Hooke’s Law to study objects such as springs and elastic cords, and this video will discuss how we do that, and also the meaning of the spring constant. We will have a brief look at the typical force-extension graphs of objects and discuss the limit of proportionality.

In the GCE A Levels, it is possible to study systems where different springs are connected in parallel or series systems. This video will discuss how to tackle such problems and how to combine the various spring constants into one effective spring constant.

While pressure is not explicitly taught in the GCE A Levels, we do require a solid understanding of it. This video will revise the concept of pressure, and how to deal with pressure due to fluids.
One of the more interesting forces introduced in the GCE A Levels is upthrust. This video will show you how upthrust comes about from the pressure differences of an immersed object, and will also show how that leads to the famous Archimedes’ Principle.
One interesting phenomenon we observe is that some objects sink, while others float in different fluids. The GCE A Levels requires us to understand why this happens, and this video will show how the balance between upthrust and weight, can lead to explaining how the relative densities of objects and fluids can decide this matter.
This video will discuss what free body diagrams are, and how to draw good and accurate ones. I n the GCE A Levels, you may be asked to draw graded FBDs, but usually we draw sketches of it to analyse the forces on a mass.
One of the types of equilibrium we study in the GCE A Levels is translational equilibrium. This video will describe a systematic way to breakdown such problems.
To study the rotational equilibrium of an object, an essential quantity to be able to calculate is the moment of a force. In the GCE A Levels, we are often required to calculate moments and this video will describe how that is done.
A unique case of forces creating a turning effect is when we have a couple. The GCE A Levels requires us to know what a couple is, and also how to calculate the torque created by a couple about a pivot.
One of the types of equilibrium we study in the GCE A Levels is rotational equilibrium. This video will describe a systematic way to breakdown such problems.