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Center of Gravity of Moving Objects

Teacher Toolbox icon Teacher Toolbox - The Purpose of this Reading

This reading is intended to provide examples as to why the center of gravity (CoG) is important by considering a cargo truck that drives around bends or slopes and how the weight of the cargo can affect the CoG.

A sign warning trucks to slow down or risk tipping over

Balancing Gravity and Other Forces

Consider the truck shown on the sign. Trucks that carry heavy loads are often taller than they are wide. Even so, if the truck's center of gravity (CoG) stays above the wheels, the truck will stay upright.

As the truck moves, changes in the slope or pitch of the road will affect the pull of gravity on the truck's CoG. So will the truck's inertia. Inertia is the resistance an object has to change in its current state of motion or velocity. If the truck goes quickly around a curve, inertia will cause the mass of the truck to pull to one side. If these effects are strong enough, the wheels will no longer be under the CoG, and the truck will topple over.

Consider these factors, and how they affect a truck's CoG:

  • Does the truck's CoG move as more weight is added to its cargo?

  • If so, in which direction?

  • How does the placement of cargo inside the truck affect the truck's CoG?

  • What happens if the cargo is able to slide or roll around inside the truck?

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The truck's CoG does move somewhat as more weight is added to its cargo. It moves downward closer to the wheels. The placement of cargo could negatively affect the truck's CoG if it is placed on only one side of the truck and is piled high. Instead, cargo should be placed in an even distribution and not be any higher than necessary. If the cargo slides or rolls, the CoG will move with it. If this movement is too extreme and the CoG is no longer above the wheels, the truck is likely to topple.