Principle of lever: In every balanced condition the product of weight and the weight arm is always equal to the product of effort and effort arm. This principle can be represented by weight x weight arm = effort x effort arm W x d = E x D The length of the effort arm is large which requires lesser effort for lifting a known weight. Because of this reason it becomes easier to lift or slide heavy object with the help of a crowbar. Therefore, we can say that with the help of a lever a greater force can be exerted at a point by applying a small force at some other point.