Pushcarts - Forces

How has it been done before?

Engineering Facts

A force is a push or pull. Forces have direction (up, down, sideways) and size (large force or small force).

Learn more about forces!

There are two forces you will need to recognize in the design of the pushcart frame. Those forces are weight and friction.

Weight is a force caused by the effect of the Earth's gravity on the mass of the driver and the cart. Mass is the technical name for the stuff (material) of which the cart and the driver are made. The weight acts down through the centre of gravity of the pushcart.

The wheels support this force. The frame and wheels must be strong enough not to break under the combined weight of the frame itself, the seat and the driver. Also the wheel mounts (how you have fastened the wheels to the frame) must be able to support the weight without breaking.

How will you test your pushcart to see whether it can take the weight without breaking? Can you use models? If not, why not?

When you come to drive your pushcart, you will find that the wheels and wheel mounts will have to handle even bigger forces than just weight. These extra forces are the dynamic forces of a moving vehicle. All these forces together are called the load.

Forces from loads or movement will either:

• squash a structure or part of it (compression forces)
• stretch it (tension forces)
• bend it (bending forces)
• twist it (torsion forces)
• cut it (shearing forces)

Suggestions and Choices

Try This

Use your imagination. Sit on your chair or the floor and pretend you are driving a very fast racing car. Hold the steering wheel and drive in a straight line very fast.

Oops! There is a sudden bend in the track. Sharp right! Steer into it quickly!

Did you lean your body into the bend? You probably did. Why?

Next time you go for a drive in a car close your eyes and feel what happens when you don't see the bend coming and you don't lean your body into the bend. What happens to your body? The better the suspension in the car, the less you will feel the forces that actually throw you away from the bend.

The wheels on the outside curve of the bend need to overcome all these forces and keep your pushcart on the road. You can help by leaning into the curve as you steer.

For Teachers

The forces that make up the load. These forces come from the interaction between friction of the wheels on the ground, pushing the cart (called the thrust) and the  cart's weight.