Last edited 26 Oct 2018

### Main author

Nathan Massey Website

#  How do Lifts Work?

A lift uses physical mechanisms that work together to lift or lower a car to various floors. The key components of a lift system include one or more car, a counterweight, an electric motor, metal cables, and various security systems.

Each part plays a particularly important part in the role of a lift system, and there are a lot of physical principles that are considered to ensure the lift stays functional and as safe as possible.

#  Conservation of Energy

This principle is one of the most widely known physical laws that is used. The law states that the total energy of a system that doesn’t interact with its surroundings remains constant. It is also referred to in the following statement:

Energy is neither created nor destroyed; it transforms from one form to another.”

This would be, for example, converting electrical energy to kinetic energy within a motor. This law is particularly important in lift design, as it helps with the understanding of the raising and lowering of a lift car. Lift cars possess gravitational potential energy (GPE), which is the energy that an object possesses depending on how far the object is from Earth.

A lift that is high up has a greater GPE than if it was lower. Gaining this GPE must come from somewhere, and it comes from mechanical or electrical energy from the motor. To lift a car, more force needs to be applied than the car’s mass times by Earth’s acceleration due to gravity.

For example, lifting a 1,000kg car would require approximately 10,000N to lift using a single pulley, which is an immense amount of force.

#  The Physics of Counterweights

Counterweights provide a way to make life a lot easier when lifting a car to higher floors. Traditionally, counterweights weigh the same as when a lift is at half capacity. For example, if a car weighed 1,000kg and has a capacity of 1,000kg, the counterweight would weigh 1,500kg.

Because of this extra weight, it means that less force and, therefore, energy is needed to lift the car. For example, if the lift car is 3,000kg and the counterweight is 2,000kg, then 1,000kg is needed to be lifted as opposed to 3,000kg – an energy reduction of 66.7%.

Because of how they are implemented, it also means that the counterweight increases the acceleration that is required to raise the lift and decreases the acceleration that is required to lower the car, all of which helps to lower the amount of energy that is required by the motor.

As well as this, counterweights help to reduce the amount of energy that is used by the motor, which is beneficial in terms of increasing the environmental friendliness of lift systems. The goal is to ensure that the least amount of energy is used, whilst also maintaining the most efficient service possible.

#  Related articles on Designing Buildings Wiki

--Nathan Massey 14:38, 11 Jul 2017 (BST)