Transcript TAKS Review - Greenslime

STAAR Review
Category 2-Force, Motion, & Energy
Students demonstrate an understanding
of force, motion, and energy and
their relationships.
Transformation of Energy
• What forms?
– Heat, chemical, mechanical, & electrical
• Creating electricity from?
– geothermal, wind, burning of fossil fuels,
hydroelectric, nuclear, etc. by changing
forms
• Law of Conservation of Energy?
– energy is neither created nor
destroyed, it changes forms
6.9C
Transformation of Energy
• Potential
– Stored energy based on position; energy
that can do work
• Kinetic
– Energy of motion; energy doing work
On the next slide, explain where
the ball has potential and kinetic
energy. Also, where is kinetic
energy the lowest and the highest?
6.8A
Height (cm)
Ball Bounce Height over Time
6.8A
Time (s)
Newton’s Laws
• 1st – Law of Inertia
– objects in motion stay in motion at a constant
velocity and objects at rest stay at rest unless
another forces acts on it
• 2nd – Law of Acceleration
– Acceleration = force applied to an object
divided by its mass (a = F/m OR F = ma)
• 3rd – Law of Action-Reaction
– for every action force, there is an equal but
opposite reaction force
8.6C
Balanced vs. Unbalanced
• Balanced forces result in…
– Objects at rest staying at rest
– Objects in motion stay in motion at a
constant velocity
• Unbalanced forced result in…
– Resting objects caused to move
– Objects in motion change their speed
and/or direction
8.6A
Motion Terms
• Force A push or pull on an object;
has a size and direction
• Motion Movement; change in an
object’s position over time
• Speed Distance traveled over time;
distance divided by time
• Acceleration
8.6B
Change in speed over time;
change in velocity divided by
time to make change; + (speed
up) or – (slow down)
Calculations
• A car has a mass of 900 kg. It
travels 600 m in the same direction
for 30 s at a constant speed. What
is its speed?
Speed = d/t = 600 m/30 s = 20 m/s
• What is its acceleration?
Acceleration is a change in speed or
direction; since the car is traveling
at a “constant speed” & does not
turn, its acceleration is zero.
8.6A; 6.8C
Calculations
• A rock is thrown from a bridge 15 m
above the river with a 2.5 N force.
It has a mass of 0.5 kg. What is the
acceleration of the rock?
F = ma
25 N = 0.5 kg x a
a = 25 N / 0.5 kg
a = 50 m/s2
8.6B
REMINDER
1 N = 1 kgm/s2
Calculations
• A Southwest airplane travels at a
rate of 7 km/min at a height of
18,000 m above the Earth’s surface.
How long will it take to travel from
Dallas to San Antonio which is 315 km
away?
Speed = d / t
7 km/min = 315 km / t
t = 315 km / 7 km/min
t = 45 min
8.6A; 6.8C
Calculations
• It is 475 km from Dallas to San
Antonio. How long will it take you to
drive from Dallas to San Antonio if
you average 100 km/h in a car with a
mass of 950 kg?
Speed = distance ÷ time
100 km/h = 475 km ÷ t
t = 475 km ÷ 100 km/h
8.6A; 6.8C
t = 4.75 h
Reminders…
• Energy is not created nor destroyed; it
is only converted from one form to
another; i.e., chemical  heat 
mechanical  electrical
• Potential energy is energy of position;
kinetic energy is energy of motion
• Forces affect motion, speed, &
acceleration
»Any questions???