1. Category 2-Force, Motion, & Energy
STAAR Review
Category 2-Force, Motion, & Energy
Students demonstrate an understanding
of force, motion, and energy and
their relationships.
READINESS Standards:
8.6A— Application Level 3: Demonstrate and calculate how unbalanced forces change the speed or direction of an object’s motion;
8.6C— Analysis Level 4: Investigate and describe applications of Newton’s law of inertia, law of force and acceleration, and law of action-reaction such as in vehicle restraints, sports activities, amusement park rides, Earth’s tectonic activities, and rocket launches.
SUPPORTING Standards:
8.6B— Analysis Level 4: Differentiate between speed, velocity, and acceleration;
7.7A— Analysis Level 4: Contrast situations where work is done with different amounts of force to situations where no work is done such as moving a box with a ramp and without a ramp, or standing still.
6.8A— Comprehension Level 2: Compare and contrast potential and kinetic energy;
6.8C— Application Level 3: Calculate average speed using distance and time measurements;
6.9C— Application Level 4: Demonstrate energy transformations such as energy in a flashlight battery changes from chemical energy to electrical energy to light energy.
6.11B – Comprehension Level 2: Understand that gravity is the force that governs the motion of our solar system;

2. 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
Have students give examples of changing forms of energy; i.e., How a flashlight works-> chemical energy stored in batteries is converted to electrical energy which pass through the wire of the light bulb creating light energy (& wasted heat energy).
6.9C

3. 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

4. Ball Bounce Height over Time
Greatest potential energy = ball at 0,100 (before first drop)
Greatest kinetic energy = moment it just as it begins to touch the floor for the 1st time
Potential energy occurs at every peak (crest) and at the bottom of each valley (trough) at the point which the ball stops going down and before it starts going up
Kinetic energy occurs at every point between the peak (crest) and valley (trough)
Kinetic energy increases as the ball moves from peak to valley and decreases again as it nears the next peak
Height (cm)
Time (s)
6.8A

5. Newton’s Laws 1st – Law of Inertia 2nd – Law of Acceleration
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
At this point, discuss with students how these laws affect the motion of everyday things; i.e., why seat belts do their job—1st law…body wants to keep going when car stops quickly…being tied to the car allows the body to “become part of the car” and slow down with it; 3rd law applies to a rocket engine…inside the engine, there is an explosion that applies force in all directions…however, since there is nothing for the force to push on at the bottom of the engine it exits as exhaust (action force)…the reaction force is being applied to the top of the engine…since this is unbalanced, the engine (and therefore the rocket) move upward.
8.6C

6. 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
It is VERY important that students understand that a moving object CAN have balanced forces if it is maintaining a constant velocity. Further, make sure students understand that when there are unbalanced forces, the object will move in the direction of the greatest force.
8.6A

7. Motion Terms Force Motion Speed Acceleration
A push or pull on an object; has a size and direction
Force
Motion
Speed
Acceleration
Movement; change in an object’s position over time
Distance traveled over time; distance divided by time
Change in speed over time; change in velocity divided by time to make change; + (speed up) or – (slow down)
8.6B

8. 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?
What is its acceleration?
Speed = d/t = 600 m/30 s = 20 m/s
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

9. 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
REMINDER
1 N = 1 kgm/s2
8.6B

10. 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

11. 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?
STAAR will most likely have extra information in most questions.
Speed = distance ÷ time
100 km/h = 475 km ÷ t
t = 475 km ÷ 100 km/h
t = 4.75 h
8.6A; 6.8C

12. Reminders… Any questions???
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???