Transcript Kinetic Energy - Welcome to NLCPHS

Calculating Energy
What did you notice about the TOTAL
ENERGY during the skatepark lab?
• Total Energy does NOT change!
• The amount of KE, PE and THERMAL
change, but always add up to the
same total!
THE LAW OF CONSERVATION
OF ENERGY:
Energy cannot be created or destroyed,
it only changes forms
Potential Energy
Stored Energy
Any energy that is STORED UP is
Potential Energy!
• Gravitational PE
– Determined by an object’s height
• Elastic PE
– Stretching or Compression
• Chemical PE
– Food (not yet eaten)
– Gasoline (not yet burned)
– Battery (not yet used)
Gravitational PE
• Any time an object has height above a
reference point.
• GPE = M*G*H
– Mass (in kilograms)
– G (acceleration due to gravity = 9.8 m/s2)
– Height (in meters)
The UNIT for Energy is JOULE (J)!
EXAMPLE 1
• A 0.5-kg squirrel sits at the top of a 10meter tall tree eating an acorn. How
much Gravitational Potential Energy
does the squirrel have?
Step 1: Write the given information and the formula
M = 0.5 kg
H = 10 m
G = 9.8 m/s2
GPE = mgh
Step 2: Substitute the given values into the formula
GPE = 0.5kg x 9.8 m/s2 x 10 m
Step 3: Solve the problem (with units!)
GPE = 49 Joules
Practice on Your Own
1. Nijah drives her 1000-kg Mini Cooper to
the top of a hill 7 meters tall. How much
GPE does the Mini have at the top of the
hill?
2. Ronnie throws a 1-kg football straight up
in the air. How much GPE does the
football have when it is 9 meters high?
3. Keanna jumps on a trampoline. If she has
a mass of 65 kg and jumps 5 meters into
the air, how much GPE can she obtain?
Kinetic Energy
Energy of Motion
Which has more kinetic energy:
• A falling ping pong ball
or
• A falling bowling ball?
• Increasing mass increases KE!
• How do you get your bike to
go really really fast down a
hill?
• Increasing speed increases KE!
How much kinetic energy an object
has depends on 2 things:
• Its MASS (kg)
and
• Its VELOCITY (m/s)!
KE = ½ * M *
2
V
The UNIT for Energy is JOULE (J)!
EXAMPLE
• A 3000 kg delivery truck drives down
the street at 15 m/s. How much
Kinetic Energy does it have?
Step 1: Write the given information and the formula
M = 3000 kg
V = 15 m/s
KE = 1/2mv2
Step 2: Substitute the given values into the formula
KE = ½ x 3000kg x (15 m/s)2
Step 3: Solve the problem (with units!)
KE = ½ x 3000kg x 225 = 337,500 J
Practice on Your Own
1. Debra pedals her bike at 20 m/s. If she and
her bike have a mass of 100 kg, how much
KE does she have?
2. A 6-kg alley cat is chasing a mouse at a
speed of 4 m/s. How much KE does the
cat have?
3. Timara kicks a 1.5-kg soccer ball giving it a
velocity of 3 m/s. How much KE does the
ball have?