Question

How does work affect energy between objects so it can cause a change in the form of energy?

Work transfers energy.
Work increases energy.

Answer 1

Short answer: Work is the mechanism by which energy is transferred between objects or systems. When a force acts over a displacement it transfers energy; that transferred energy appears as a change in some form of energy (kinetic, potential, thermal, internal, chemical, etc.). Whether an object's energy increases or decreases depends on the direction of the force and which body does the work.

Key points and simple formulas
- Definition: Work done by a (constant) force F through a displacement Δx in the direction of the force is W = F·Δx (more generally W = ∫ F·dx).
- Work is an energy transfer. Positive work on a body increases that body’s energy; negative work reduces it.
- Work–energy theorem (single particle): net work done on an object = change in its kinetic energy,
W_net = ΔK.
- For systems with potential energy, conservative forces convert between kinetic and potential energy without net loss; nonconservative forces (friction) convert mechanical energy into internal (thermal) energy. For a system,
ΔE_mech = W_nc,
where ΔE_mech = ΔK + ΔU and W_nc is work by nonconservative forces.
- Work and heat are both ways to transfer energy; they are path-dependent (not state functions).

Examples
- Lifting a mass: You do positive work against gravity; the mass’s gravitational potential energy increases by the work you did (neglecting kinetic change).
- Pushing a block on a frictionless floor: Your push does positive work → block’s kinetic energy increases.
- Sliding a block with friction: Your push does work that partly increases kinetic energy and partly is dissipated by friction; friction does negative work and converts mechanical energy into thermal energy (heats the block/surface).
- Compressing a gas in a piston: Work done on the gas increases its internal energy (temperature rises) if heat is not removed.

Sign convention and who loses energy
- If work is done by the surroundings on the system, the system’s energy increases (positive W_on-system).
- If the system does work on the surroundings, the system’s energy decreases (negative W_on-system).
- Energy is conserved overall: energy lost by one body through doing work is gained by another (possibly in a different form).

Microscopic view
- Macroscopic force × displacement transfers organized energy (e.g., kinetic) into microscopic degrees of freedom (internal energy) when dissipative forces act. That’s why rubbing your hands (doing mechanical work) heats them.

If you want, I can show a short numerical example (e.g., a block accelerated by a force, or work done compressing a gas) to illustrate the arithmetic.