Conservative forces are associated with a potential energy. The gravitational force that gives rise to the potential energy of child 1 at the top of the ramp is conserved, in a sense, as she converts it to kinetic energy during her trip down to the lake surface.

Friction has no associated potential energy, and so is considered nonconservative.

Friction is a non-conservative force, meaning that the work it does depends on the path taken by the object. For example, moving a brick in a long zig-zag across the table will generate more heat from friction than moving it in a straight line across the table.

Electric and gravitational forces are conservative. This can be tested by knowing a constant equation to calculate the energy associated with these forces; such equations are applicable regardless of path. No such equation exists for frictional energy.

Air resistance is a form of friction that acts in the direction opposite motion, slowing down an object. If the ball spends less time in flight, it will travel less of a distance, requiring the cushion to be placed closer to the launch position.

While one might expect the "weak" force to be the weakest of the four universal forces, the gravitational force is actually several orders of magnitude weaker than the weak force.

In order from strongest to weakest, the fundamental forces are the strong (nuclear) force, electromagnetic force, weak force, and gravitational force.

Conservative forces are forces that do not lose energy to heat, sound, or light. Of these answers, energy is completely conserved and transferred from kinetic energy to potential energy, or vice versa. Gravitational forces, electrostatic forces, and elastic forces all work by providing a potential that will work in the same direction as the motion of an object or particle, allowing kinetic and potential energy to interconvert. Frictional forces lose energy as heat when sliding across a surface, and the more force (the more rough the surface), the more energy that is lost.

One-half of the force will be required to pull the platform up in the new scenario. In the diagram below, now notice that the box has two upward tension forces due to the pulley attached directly to the box. These two tension forces act against the weight of the box, meaning that each tension force is one half of the weight of the box. Because tension is transmitted unchanged over the length of the rope, the tension a person would need to pull against would be half the weight of the box. This leads us to determine that half the force would be required to lift the box if two pulleys were used.

The question states that:

Recall that the passage states that  is also one third of .

The force exerted by student Y and student Z is the same.

Mechanical advantage is defined as:

The weight of the object is the same for both students because both of them are lifting the same boulder. The force applied is also the same; therefore, mechanical advantage for both machines is the same.

The definition of mechanical advantage is:

Rearranging this equation and solving for weight gives:

Mechanical advantage is a unitless quantity. Remember the difference between weight and mass. Weight is a measure of force and has units of Newtons, whereas mass has units of kilograms.

Conservation of energy is the key here. Initial energy is all gravitational potential energy:

Note that the final height change is equal to the height above the spring added to the displacement of the spring.

This is equal to the final energy, which is all spring potential energy:

Set these equations equal and solve for the spring constant.