STAAR STAAR ReviewReviewSTAAR STAAR ReviewReview

Category 2-Force, Motion, & EnergyCategory 2-Force, Motion, & EnergyStudents demonstrate an understandingStudents demonstrate an understanding

of force, motion, and energy and of force, motion, and energy and their relationships.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

• Potential– Stored energy based on position;

energy that can do work

• Kinetic– Energy of motion; energy doing work

Transformation of Energy

On the next slide, explain where the ball has potential and kinetic

energy. Also, where is kinetic energy the lowest and the

highest?

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

6.8A Time (s)

Heig

ht

(cm

)

Ball Bounce Height over Time

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

• Motion

• Speed

• Acceleration

A push or pull on an object; has a size and directionA push or pull on an object; has a size and direction

Movement; change in an object’s position over timeMovement; change in an object’s position over time

Distance traveled over time; distance divided by timeDistance 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)

Change in speed over time; change in velocity divided by time to make change; + (speed up) or – (slow down)

8.6B

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/sSpeed = 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.

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

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

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

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

t = 4.75 h

Speed = distance ÷ time

100 km/h = 475 km ÷ t

t = 475 km ÷ 100 km/h

t = 4.75 h8.6A; 6.8C

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???