Download Kinetic energy - Mrs. Wiedeman

Chapter 4
Energy
What is energy?
Def: ability to cause change
 Every change involves energy

Different Forms
Electrical
 Chemical – stored in food, involved in
reactions
 Radiant – gives off
 Thermal – heat
 Same thing just different forms

Kinetic Energy
Def: energy of a moving object
 Depends on mass and speed


Kinetic energy (Joules) = 1 mass (kg) x [speed (m/s)]2
2
KE = 1 mv2
2
 SI unit for energy is joule (J)

Practice!
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?

Potential Energy
Even motionless objects have energy
 Stored in the object, has potential to
change
 Def: stored energy

Elastic Potential Energy
Def: stored energy by something that can
stretch or compress
 Stretched rubber band – elastic potential
energy  kinetic energy

Chemical Potential Energy
Def: energy stored in chemical bonds
 Food, gasoline, etc.

Gravitational Potential Energy

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 GPE of a .3 kg coffee mug on a
1-m high counter.

What could you do to change GPE?
 Change height or mass

Section 2
Conservation of Energy
Changing Forms of Energy
Changing electrical energy – electricity – light
and heat energy
 Energy is constantly changing forms

Transforming Chemical Energy
Cars – MANY energy transformations
 Spark plug – gasoline – engine - wheels

Transforming Chemical Energy

Green plants – take in sunlight and
transform to chemical energy in plants
Mechanical Energy

Def: total amount of potential and kinetic
energy
Mechanical Energy = Potential + Kinetic
Falling Objects

As potential  kinetic
mechanical energy
stays same

Potential lost = kinetic
gained
Projectile Motion
Mechanical energy remains constant
 Still see transformations of energy

Swinging

Best part is falling
from highest point

High GPE = Low KE

Describe transition…
Law of Conservation of Energy
Def: energy can not be created or destroyed
 Energy just changes form
 All energy in the universe does not change
 Energy in = Energy out

Is energy always conserved?
Swinging – you eventually will stop – where
does all the energy go?
 Friction – air resistance = thermal energy

Human Body – Energy Relations
What forms of energy are in your body?
 Conservation of energy still true
 Food, fat = potential energy
 Activity = kinetic energy
 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
 Faster = more kinetic energy

Temperature
Def: measure of average kinetic energy
of particles
 High Temp. = High Energy
 Low Temp. = Low Energy
 Unit  Kelvin

Thermal Energy
Collisions between air and butter particles
increase energy of butter = higher temperature
 Def: sum of kinetic and potential energy of
particles in object

Thermal Energy
As temp increases = thermal energy increases
 If object has MORE MASS and at the same
temp. has HIGHER thermal energy

Heat
Is your seat toasty?
 Def: thermal energy that flows from
something at a higher temp to a lower
temp
 Unit: Joule

Beachin’ it up!
How can there be extreme differences in
temperature from air, sand and water?
 Sun rays are the same why different
temp?
 Sand heats up 6 times faster than water

Specific Heat

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
 Strong bonds have to be broken before particles
move really fast
