Bowmen of Skelmersdale

Bow Mass and Inertia

Weight, mass and inertia are different things. The differences are explained below, but unless you intend tuning bows on the moon, the distinction is not very important.

The main point to be aware of is that more mass makes things harder to move, and not just because gravity pulls them towards the floor. They are harder to move sideways as well.


Weight is the force gravity exerts on things. It always acts towards the ground.

Weight, and the way it is spread around a bow, is responsible for the bow’s balance in the hand and the effort needed to hold the bow up.


Mass is the amount of material. Because (on Earth) weight is proportional to mass,it is usually expressed as a weight (!).

The distinction is easier to see in films of astronauts in space  they weigh less, but have the same mass.

Since it’s the amount of mass that controls how hard you need to push something to move it, mass is important when stabiliser effects are considered.


Inertia is how we describe the difficulty of moving an object. It’s another way of thinking about the effect of weights. Isaac Newton’s view would be that, because the mass is higher, the same force moves things less. Before Newton came along,

Inertia was a force that resisted movement. So we commonly use ‘high-inertia’ to describe a stabiliser system that is hard to move quickly. That may not only be due to the amount of mass; a very rigid system is harder to move a small distance than a

flexible one.

What bow behaviour needs controlling?

Bow  movement

Timing - When is movement important?

Time and Motion

Controlling bow displacement

Weight, Mass and Inertia

Static and Dynamic properties

The misnamed TFC

Controlling bow balance

Centre of Gravity

Finding the centre of gravity

Changing the balance using weight

Weights and Distances

Rods, weights and risers

Controlling bow vibration

Causes of Bow Vibration

Reducing Vibration - Damping

Bow Resonance

Tuned damping - more on TFC’s