Force, Motion and Energy

Force, Motion and Energy Test Thursday, November 15
The Answer Key is an attachment. Look to the left if you need to print or see the diagrams.

Unit 3 Review

Force, Motion & Energy

 

Make sure you know the 26 vocabulary terms.

 

1. Acceleration: The rate at which the velocity of an object changes-speed up, slow down &/or change in direction

2. Balanced forces: forces that cause no change in an object's motion.

3. Displacement: the change in position of an object; shortest distance from one point to another point

4. Elastic potential energy: the stored energy of an object that is stretched or compressed

5. Energy: the ability to do work.

6. Energy transformation: A change from one form of energy to another

7. Exhaustible: capable of being used up; nonrenewable

8. Force: A push or pull on an object

9. Friction: the force that opposes the motion of one surface as it moves across another surface

10. Gravitational potential energy: stored energy that depends on the height of an object

11. Inertia: the tendency of an object to resist a change in its motion

12. Inexhaustible: incapable of being entirely consumed or used up; renewable

13. Joule: SI unit of energy

14. Kinetic energy: The energy of a moving object

15. Law of Conservation of Energy: That energy can neither be created nor destroyed

16. Momentum: the force or speed with which something moves; the force or speed with which something moves

17. Motion: any change in an object's position

18. Net force: combination of all forces acting on an object

19. Newton: the SI unit of force; N

20. Newton's First Law of Motion: Law of Inertia: An object at rest will remain at rest unless an unbalanced force acts upon the object. An

object in motion will remain in motion at the same speed and direction unless an unbalanced force acts upon the object.

21. Newton's Second Law of Motion: The acceleration of an object is directly proportional to the force acting on the object, but inversely

proportional to the mass of the object; F=mass x acceleration

22. Newton's Third Law of Motion: Every action has an equal and opposite reaction.

23. Speed: the distance an object travels in a certain amount of time; s=d/t

24. Unbalanced forces: forces that cause the motion of an object to change-speed up, slow down or change direction

25. Velocity: The speed of an object moving in a particular direction

26. Work: When you exert a force on an object that causes the object to move. Work can be thought of as the transfer of energy.

 

 

1. How does the mass of a body at rest affect its tendency to remain at rest?

Newton’s law of inertia states that an object at rest stays at rest. An object with more mass has a greater tendency to resist changes in its state of motion.

 

2. How does the force required to move an object change with mass?

The greater the mass or acceleration an object has, the greater the force of that object. Also, a larger force must be exerted on an object with greater mass in order for it to have the same acceleration as an object with less mass.

 

What is a force?

A force is a push or pull that can change the motion of an object

 

3. How does the force acting on an object affect its tendency to remain at rest?

The less force, the greater the tendency to remain at rest. The object will move if the forces become unbalanced. It will move in the direction with the greater force applied.

 

4. Explain the difference in words and with a diagram between unbalanced and balanced forces.

Balanced forces-object will not move or will remain moving at a constant speed

Unbalanced forces-object will move in same direction of greatest force

Forces are balanced when there are equal forces exerted in opposite directions. These forces are balanced and cancel each other out. (Objects at rest or moving at a constant speed)

Forces are unbalanced when two or more unequal forces act upon an object in opposite directions; the net force is determined by calculating the resultant of the forces. The object will move in the direction of the stronger force.

 

5. What are 2 examples of exhaustible resources and 2 examples of inexhaustible resources?

Coal, Oil and Natural Gas are examples of exhaustible resources

Solar energy, wind and water are examples of inexhaustible resources

 

 

6. Describe net force using an example.

Text Box: Force of Mrs. Payne’s arm (250 N)

 

Text Box: Net force = 50 N upwards

 

 

Text Box: Force of gravity (200N)

 

 

 

7. How does mass affect the speed of an object?

 

Speed is only a measure of how fast something is traveling and bears no relation to the size, shape or mass of an object (speed = distance/time). However, mass does affect momentum (momentum = mass x velocity) so an object with a high mass will take more force to stop.

 

8. What are 2 real world examples of elastic potential energy and 2 real world examples of gravitational potential energy?

 

Sling shot, bow for an arrow, rubber band, and a spring all are examples of elastic potential energy

Rocks at the top of a hill or water behind a dam are two examples of gravitational energy.

 

9. Sketch a roller coaster track and label the highest and lowest potential and kinetic energy points.

http://www.world-of-waterfalls.com/images/mgh2mvsq_coasterL.gif

 

 

10. Describe two examples of friction you encounter before even leaving your house in the morning.

Brushing my hair there is friction between the brush and my hair, brushing my teeth; walking across the rug, putting lotion on my face, opening the door with a throw rug in the way

 

 

11. Explain the difference between speed and velocity. How do they relate to acceleration?

Speed: how fast an object is moving-distance divided by time

Velocity: speed in a particular direction

Acceleration: rate at which an object changes its velocity-speed up, slow down or change direction

 

12. What is Newton’s 3 Laws of Motion and include an example.

1st law: An object at rest will remain at rest and an object in motion will continue in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia". EX. Need for a seatbelt-riding in a car-your body would continue traveling at the same speed your car is if it suddenly stops

2nd Law: F=ma (force=mass times acceleration); Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). EX. A bowling ball will need more force to accelerate at the same rate as a tennis ball

3rd Law: Force every action force there is an equal and opposite reaction force; EX. A rocket taking off; the seatbelt would act as the opposite force

 

13. Be able to calculate work using the formula, W=F x d: If a car is towed 4 km to a dealership using a force of 1800 N, how much work is done?

1 Joule= 1 Newton-meter

4 km=4000m

W=1800 N x 4000m

7,200,000 J= 1800 N x 4000m

 

14. Be able to calculate speed using the formula, s=d/t: If a car travels 400m in 20 seconds, how fast is it going?

 

400m/20s=20 m/s

 

15. Be able to calculate opposing force in Newton's Second Law, a 5kg block is pulled across a table by horizontal force of 40 N with a frictional force of 8 N opposing the motion. Calculate the acceleration of the object.

Force=mass times acceleration

40 N – 8 N = 32 N

32 N = 5 kg x ____; 32/5=

A=6.4 m/s2

 

16. What is the energy transformation in photosynthesis?, coal plant?, digestion, a windmill?, a battery operated CD player, a siren, a car engine?

 

Photosynthesis-radiant (sun) to chemical (sugar)

coal plant-chemical to thermal to mechanical to electrical

wind turbine-mechanical to electrical

a battery operated CD player-chemical to electrical to mechanical to sound

a car engine-chemical (gas) to mechanical (kinetic)- to move gears, cylinders, axles, wheels etc; also thermal & sound energy; chemical (batteries) to electrical to mechanical

digestion-chemical (food) to mechanical

 

 

Interpreting Graphs

A distance-time graph tells us how far an object has moved with time-SPEED

The steeper the graph, the faster the motion.

A horizontal line means the object is not changing its position - it is not moving,

it is at rest.

A downward sloping line means the object is returning to the start.

 

A speed - time graph shows us how the speed of a moving object changes with time-ACCELERATION

The steeper the graph, the greater the acceleration.

A horizontal line means the object is moving at a constant speed.

A downward sloping line means the object is slowing down.

 

 

 

 

 

 

 

Look at the graph above. It shows how three runners ran a 100-meter race.

 

Which runner won the race? Explain your answer.

 

ALBERT WON-HE FINISHED IN 12 SECONDS; BOB-14 SECS; CHARLIE-17 SECS

 

Which runner stopped for a rest? Explain your answer.

 

CHARLIE-the straight, horizontal line indicates he wasn’t moving-no increase in distance

 

How long was the stop? Explain your answer.

 

5 seconds; because 13 seconds minus 8 seconds equals 5.

 

How long did Bob take to complete the race? Explain your answer.

 

BOB-14 SECS

 

Calculate Albert’s average speed. (Figure the distance and the time first!)

 

100 meters divided by 12 seconds=8.3 m/s

Bob-7.14 m/s

Charlie-5.88 m/s

 

 

The graph below shows how the speed of a bus changes during part of a journey

 

 

Choose the correct words from the following list to describe the motion during each

segment of the journey to fill in the blanks.

 

accelerating

decelerating

constant speed

at rest

 

Segment 0-A The bus is ____ accelerating ______. Its speed changes

from 0 to 10 m/s in 5 seconds.

Segment A-B The bus is moving at a ____ constant speed ______________of 10

m/s for 5 seconds.

Segment B-C The bus is ________ decelerating ____________. It is slowing

down from 10 m/s to rest in 3 seconds.

Segment C-D The bus is _____ at rest _____________________________. It has

stopped.

Segment D-E The bus is ________ accelerating ______________________.

It is gradually increasing in speed.