Physics Unit 3

Work

done to an object when a force displaces the object in the direction of the force or a component of the force; can only be determined if a constant amount of force is applied

Units: J

2 cases when no work is done

if the force is perpendicular to the displacement and if force is applied but no displacement occurs

positive work

when the force is in the same direction as the displacement

negative work

when the displacement and force are in opposite directions

area underneath a force-position graph represents…

work

energy

capacity to do work

kinetic energy

the energy of a moving object

Potential energy

energy stored in a non moving object

gravitational potential energy

energy stored by an object due to its position relative to the surface of the earth

work-energy principle

the change in Ek = Work, so if there is a change in energy, there must be work being done

mechanical energy remains constant in…

a system with no external forces

Hooke’s Law

The amount of force exerted by the spring is proportional to the displacement of the spring. applies to anything that can be stretched or compressed

Restorative Force

the force a spring exerts which is opposite to the direction of the applied force

Ideal Spring

any spring that obeys Hookes law (has no external or internal force)

spring force is proportional to

displacement

Elastic Potential Energy

energy stored in objects that are compressed or stretched

determined by calculating the change in kinetic energy (work)

Linear Momentum

a vector quantity that describes the motion of an object travelling in a straight line as the product of its mass and velocity

kg\*m/s

momentum is proportional to…

mass and velocity

Impulse

the product of force and time that acts on an object to produce a change in momentum

N\*s

a small force for a long time yields _____________ impulse as a large force for a short time

the same

total energy in an isolated system must…

stay constant

Mechanical energy

the sum of all the energies in a system

____________ and ____________ are always conserved in a collision

total energy and total momentum

Inelastic Collisions

momentum is conserved but kinetic energy is not

Perfectly Inelastic Collision

an ideal collision where 2 objects stick together perfectly so that they move with the same final velocity

Elastic Collisions

both kinetic energy and momentum are consderved

Perfectly Elastic Collision

an ideal situation where friction and other forces are negligible

Efficiency

the ratio of the amount of useful energy produced to the amount of energy used, expressed as a percent

Power

The rate at which energy is transformed, or the rate at which work is done

* speed of energy transformation

J/s = W

1 kWh =

3\.6 x 10^6 J

Kinetic Molecular Theory

Based on the premise that matter is made up of small particles, known as atoms and molecules, that attract each other, and that all possess kinetic energy.

An increase in the motion of the particles of a substance makes the substance feel warmer; a decrease in motion makes the substance feel colder.

the greater the space between molecules the greater the ________

energy

Thermal Energy

the total amount of kinetic (motion of particles) and potential (attraction between particles) energy possessed by the particles of a substance

Temperature

measure of the average kinetic energy of the particles of a substance

SI Units: Celsius

Heat

describes the transfer of thermal energy from a substance with higher temperature to a substance with lower temperature

same temperature does not mean same _____________

thermal energy

Celsius is based off…?

the temperature at which water freezes and boils

State changes

Methods of transferring thermal energy

1. conduction
2. convection


1. radiation

Thermal Conduction

the transfer of thermal energy that occurs when warmer objects are in physical contact with colder objects

Convection

When colder, denser fluids fall and push up warmer, less dense fluids

Applies to liquids and gases

Radiation

transfer of thermal energy through electromagnetic waves

Thermal Conductors

materials that allow thermal energy to pass through them relatively easily and quickly. Materials with low heat capacities

Specific Heat Capacity

the amount of energy needed to raise the temperature of 1 kg of a substance by 1 °C

J/kg°C

Quantity of Heat

total amount of thermal energy transferred from a warmer substance to a colder substance.

J

Principle of Thermal Energy Exchange

when a warmer object comes in contact with a colder object, the thermal energy is transferred from the warmer object to the colder object until all of the thermal energy is evenly distributed in both objects.

Qreleased = -Qabsorbed (same absolute values)

Thermal Expansion

The increase in the volume of an object due to an increase in its temperature.

Thermal Contraction

the decrease in the volume of an object when thermal energy is released

Fusion

absorption of thermal energy when an object changes from a solid to a liquid

when does temperature change

when 1 state is present

why is temperature constant when states are changed

thermal energy is used to change potential energy (bonds), not kinetic energy

Latent Heat

Total Thermal energy absorbed or released when a substance changes state (J)

Specific Latent Heat

the amount of thermal energy needed for 1 kg of a substance to change from one state to another

Latent Heat of Fusion

the amount of thermal energy released when a substance freezes or absorbs when it melts

Latent Heat of Vapourization

The amount of thermal energy absorbed when a substance evaporates or released when it condenses

Why is solid water more dense than liquid

hydrogen bonding causes oxygen molecules to be more organized when frozen so they take up more space

Why is latent heat “hidden“?

thermal energy change remains hidden until the opposite state change occurs.