Forces, centre of gravity, reactions and stability

How to use this resource

Please download the PDF of this resource using the Download PDF link in the banner above.

Below are a series of interactives which support the resource. Each interactive can be launched by clicking on its image, or through links in the PDF itself.

Some resources have pre-requisites; where this is the case, you'll be able to access any required resources through the Pre-requisites section.

Topic areas

Mechancial engineering

  • Centre of gravity
  • Forces
  • Moments
  • Reactions
  • Resolving forces on an
    inclined plane


  • Angles
  • Trigonometric identities


It may be useful to look at the resource ‘Centre of gravity of composite bodies’ to introduce the concepts of the centre of gravity and tipping.

Problem statement

Many engineered objects, such as buses, boats, diggers, pushchairs, furniture, etc. are required to be resistant to tipping over under normal use conditions. How can an engineer determine when an object will tip over?


Click the image to load Tipping 1. 

The above interactive allows you to tilt an object and see at wich point it moves for being stable to tipping over.

Click the image to load Bus 1. 

The above interactive allows you to change elements of the bus and see its effects on the tipping angle.

Supported by

  • Royal Academy of Engineering
  • Motorola Solutions Foundation