Chapter 4 Energy

What is energy? Def: ability to cause change Def: ability to cause change Every change involves energy Every change involves energy

Different Forms Electrical Electrical Chemical – stored in food, involved in reactions Chemical – stored in food, involved in reactions Radiant – gives off Radiant – gives off Thermal – heat Thermal – heat Same thing just different forms Same thing just different forms

Kinetic Energy Def: energy of a moving object Def: energy of a moving object Depends on mass and speed Depends on mass and speed Kinetic energy (Joules) = 1 mass (kg) x [speed (m/s)] 2 Kinetic energy (Joules) = 1 mass (kg) x [speed (m/s)] 2 2 KE = 1 mv 2 KE = 1 mv 2 2 SI unit for energy is joule (J) SI unit for energy is joule (J)

Practice! What is the kinetic energy of a.15 kg baseball moving at 40 m/s. What is the kinetic energy of a.15 kg baseball moving at 40 m/s. A car moving at a speed of 20 m/s has a kinetic energy of 300,000 J. What is the car’s mass? A car moving at a speed of 20 m/s has a kinetic energy of 300,000 J. What is the car’s mass?

Potential Energy Even motionless objects have energy Even motionless objects have energy Stored in the object, has potential to change Stored in the object, has potential to change Def: stored energy Def: stored energy

Elastic Potential Energy Def: stored energy by something that can stretch or compress Def: stored energy by something that can stretch or compress Stretched rubber band – elastic potential energy  kinetic energy Stretched rubber band – elastic potential energy  kinetic energy

Chemical Potential Energy Def: energy stored in chemical bonds Def: energy stored in chemical bonds Food, gasoline, etc. Food, gasoline, etc.

Gravitational Potential Energy Def: stored energy by objects due to position above earth (able to fall) Def: stored energy by objects due to position above earth (able to fall)

Practice! Find the height of a.15 kg baseball that has a GPE of 73.5 J. Find the height of a.15 kg baseball that has a GPE of 73.5 J. Find the GPE of a.3 kg coffee mug on a 1-m high counter. Find the GPE of a.3 kg coffee mug on a 1-m high counter. What could you do to change GPE? What could you do to change GPE? Change height or mass Change height or mass

Section 2 Conservation of Energy

Changing Forms of Energy Changing electrical energy – electricity – light and heat energy Changing electrical energy – electricity – light and heat energy Energy is constantly changing forms Energy is constantly changing forms

Transforming Chemical Energy Cars – MANY energy transformations Cars – MANY energy transformations Spark plug – gasoline – engine - wheels Spark plug – gasoline – engine - wheels

Transforming Chemical Energy Green plants – take in sunlight and transform to chemical energy in plants Green plants – take in sunlight and transform to chemical energy in plants

Mechanical Energy Def: total amount of potential and kinetic energy Def: total amount of potential and kinetic energy Mechanical Energy = Potential + Kinetic

Falling Objects As potential  kinetic mechanical energy stays same As potential  kinetic mechanical energy stays same Potential lost = kinetic gained Potential lost = kinetic gained

Projectile Motion Mechanical energy remains constant Mechanical energy remains constant Still see transformations of energy Still see transformations of energy

Swinging Best part is falling from highest point Best part is falling from highest point High GPE = Low KE High GPE = Low KE Describe transition… Describe transition…

Law of Conservation of Energy Def: energy can not be created or destroyed Def: energy can not be created or destroyed Energy just changes form Energy just changes form All energy in the universe does not change All energy in the universe does not change Energy in = Energy out Energy in = Energy out

Is energy always conserved? Swinging – you eventually will stop – where does all the energy go? Swinging – you eventually will stop – where does all the energy go? Friction – air resistance = thermal energy Friction – air resistance = thermal energy

Human Body – Energy Relations What forms of energy are in your body? What forms of energy are in your body? Conservation of energy still true Conservation of energy still true Food, fat = potential energy Food, fat = potential energy Activity = kinetic energy Activity = kinetic energy Calorie 1C = 4,184 J Calorie 1C = 4,184 J

Chapter 6 Section 1 Temperature and Heat

Matter in Motion Matter is made of tiny particles in constant motion  have kinetic energy Matter is made of tiny particles in constant motion  have kinetic energy Faster = more kinetic energy Faster = more kinetic energy

Temperature Def: measure of average kinetic energy of particles Def: measure of average kinetic energy of particles High Temp. = High Energy High Temp. = High Energy Low Temp. = Low Energy Low Temp. = Low Energy Unit  Kelvin Unit  Kelvin

Thermal Energy Collisions between air and butter particles increase energy of butter = higher temperature Collisions between air and butter particles increase energy of butter = higher temperature Def: sum of kinetic and potential energy of particles in object Def: sum of kinetic and potential energy of particles in object

Thermal Energy As temp increases = thermal energy increases As temp increases = thermal energy increases If object has MORE MASS and at the same temp. has HIGHER thermal energy If object has MORE MASS and at the same temp. has HIGHER thermal energy

Heat Is your seat toasty? Is your seat toasty? Def: thermal energy that flows from something at a higher temp to a lower temp Def: thermal energy that flows from something at a higher temp to a lower temp Unit: Joule Unit: Joule

Beachin’ it up! How can there be extreme differences in temperature from air, sand and water? How can there be extreme differences in temperature from air, sand and water? Sun rays are the same why different temp? Sun rays are the same why different temp? Sand heats up 6 times faster than water Sand heats up 6 times faster than water

Specific Heat Specific Heat: heat needed to raise 1kg of material by 1  C Specific Heat: heat needed to raise 1kg of material by 1  C

Water as a Coolant It’s high specific heat – absorb a lot of heat without changing temp much It’s high specific heat – absorb a lot of heat without changing temp much Strong bonds have to be broken before particles move really fast Strong bonds have to be broken before particles move really fast