Download 3rd Law: Force every action force there is an equal and opposite

Unit 3 Review
Force, Motion & Energy
Make sure you know the 26 vocabulary terms.
Be able to read and interpret speed & acceleration graphs.
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 object will move if the forces become unbalance. 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.
Force is balanced — there is an equal force exerted on the block in opposite directions.
These forces are balanced and cancel each other out.
Force is unbalanced. When two forces act upon an object in opposite directions, the net
force is determined by calculating the resultant of the forces. By convention, forces to the
right (East), or up (North), are taken as positive and forces to the left (West), or down
(South), are taken as negative. 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.
Example: Mr. Whitmore lifts the heavy box over his head with one push of the arm and a force
of 250 newtons. Gravity is pulling down the mass with 200 Newtons. What is the net force and
direction of the box?
Force of Mr. Whitmore’s arm (250 N)
Net force =
50 N
upwards
Force of gravity
(200N)
7. How does mass affect the speed of an object?
Speed is only a measure of how fast something is travelling and bears no relation to the
size, shaped 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.
10. Describe two examples of friction you encounter before even leaving your house in the
morning.
Brush my hair in the morning there is friction between the brush and my curly hair, walking
across the rug, putting on 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 seatbeltriding in a car-your body would continue traveling at the same speed your car is if it
suddenly stops
2nd Law: F=ma; 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
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.