Forces and Work Done

This flashcard set helps with memorizing explanations for Unit 2 and 3 of Physics II

Hooke’s Law (equation)

F=kx

Hooke’s Law (written)

Force applied on an object is directly proportional to the strain of the object within its limit of proportionality

Spring-based Shock Absorbers (Hooke’s Law application)

To absorb shocks and vibrations from the road surface, coil springs are employed. The springs compress and store potential energy when the vehicle hits an uneven surface. By Hooke’s law, the force applied by the spring is directly proportional to the displacement, enabling the vehicle to move smoothly, ensuring passengers are comfortable.

Trampolines (Hooke’s Law application)

Trampolines utilize Hooke's Law by allowing the springs to compress when a person jumps on the surface, storing potential energy that propels them upward when the springs return to their original position.

Area under v-t graph

distance

Slope of v-t graph

acceleration

Force

push or pull

Newton’s 2nd law

F=ma

Balanced Forces

When forces acting on an object are equal in magnitude and opposite in direction, they cancel each other out, resulting in no change in the object’s motion

Deformation

A force can cause an object to change its shape temporarily (elastic deformation) or permanently (plastic deformation)

area under Force-Distance graph

Work Done

Proving proportionality

• the line on the graph is straight

• the line passes through the origin

Proving that something is constant (based on graph)

• it is constant

• the line is straight with zero gradient

Comparing f-d and v-t graphs

• find acceleration in v-t graph and use that to calculate force for the v-t graph

• compare with force in f-d graph

alternatively, compare displacements

area under power-time graph

work done

comparing p-t graph with v-t and f-d

• compare average power

• for both graphs, divide work done by time

alternatively: describe the change in power for both graphs

Law of conservation of energy

Energy can be transferred from one form to another, but the total amount must remain constant

Work-energy theorem

work done is equal to change in KE

Work

When work is done, energy must be transofmred from one form to another

Friction and Work Done

when a box is slid against a surface with friction, work is done against the box. Since there are no other external forces acting on the box, as the object deccelerates, the KE of the object is dissipated as Heat and Sound energy until it comes to rest, which is also equal to work done.

Friction, Kinetic Energy, and Work Done

the work done by frictional forces is equal to KE

Explain one factor that could affect a spring’s performance in the real-world scenario

• temperature can affect the properties of materials. A spring’s stiffness may decrease and elasticity increase as temperature increases (and vice versa). This leads to deviations from the linear relationship predicted by Hooke’s Law.

How does Work done depend on the coefficient of friction

Work done does not depend on the coefficient of friction. Work Done = change in KE, which does not vary based on coefficient of friction

How is displacement affected by the coefficient of friction

When the coefficient of friction is increased, the displacement of the object decreases. When the coefficient of friction increase, frictional force increases, meaning there is more resistance against an object’s motion. (lessened acceleration, v-t graph less distance traveled)

How does the average power depend on the coeff of friction?

When the coefficient of friction increases, the time the velocity takes to decrease to 0 decreases. Work done remains constant. Since work is constant while time decreases, Power (work done/time) will increase when the coefficient of friction increases.

Energy

Ability to do work

Chemical Potential Energy

Energy stored in a substance due to the position of the atoms or electrons in the substance. For example, food, fossil fuels, and batteries

Elastic Potential Energy

energy stored in a body due to its elastic deformation. A spring or rubber band possesses elastic potential energy when it is compressed or stretched. This energy can be converted to kinetic energy when the spring/rubber band is released.

Mechanical Energy

In physical sciences, mechanical energy is the sum of potential energy and kinetic energy.