Under the influence of gravity the body can make work. The simplest example — free fall of a body. The concept of work reflects movement of a body. If the body remains on the place, it does not make work.

## Instruction

1. Body gravity — approximately the constant equal to the work of body weight on the acceleration of gravity of g. Acceleration of gravity of g ≈ 9.8 newton on kilogram, or meter per second squared. g is a constant which size slightly fluctuates only for different points of the globe.

2. By definition, elementary work of gravity — the work of gravity on infinitesimal movement of a body: dA = mg · dS. Movement of S is function from time: S = S(t).

3. To find a job of gravity on all way of L, it is necessary to take integral from function of elementary work on L: A = ∫dA = ∫ (mg · dS) = mg · ∫dS.

4. If in a task the function of speed from time is set, then the dependence of movement on time can be found by integration. For this purpose it is required to know entry conditions: initial speed, coordinate, etc.

5. If the dependence of acceleration on t time is known, it is necessary to integrate two times, acceleration — the second derivative of movement.

6. If in a task the coordinate equation is given, then it is necessary to understand that movement reflects the difference of initial and final coordinate.

7. Besides gravity, other forces anyway affecting its position in space also can affect a physical body. It is important to remember that work — additive size: work of the resulting force is equal to the sum of works of the composed forces.

8. According to Koenig's theorem, work of force on movement of a material point equals to increment of kinetic energy of this point: A(1-2) = K2 - K1. Knowing it, it is possible to try to find a job of gravity through kinetic energy.