Transcript Motion and Machines Review

February 8, 2016
• Warm-Up: Electricity WS
• Homework: Read & take notes chapter 18,
section 3. USA Test Prep and Skills Tutor #9
due Friday by 4:15.
• Quiz Thursday: static & current electricity, AC
& DC current, series & parallel circuits
February 8, 2016
• Warm Up: start Simple Machines WS
• Homework: USA Test Prep and Skills Tutor #9
due by Friday @4:15
• Test Wednesday: Chapters 5, 6, & 8
SPS8. Students will determine relationships
among force, mass, and motion.
• a. Calculate velocity and acceleration.
– Know the difference
– Know the units
– Know how to solve the problems
– Know how to interpret the graphs
Question 1
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An object accelerates if its
A. Speed remains constant
B. Direction changes
C. Mass remains constant
D. Motion can be plotted on a graph
Question 1
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An object accelerates if its
A. Speed remains constant
B. Direction changes
C. Mass remains constant
D. Motion can be plotted on a graph
Question 2
• Which kind of forces are exerted on an object
if there is a net force of zero?
• A. Unbalanced
• B. Kinetic friction
• C. Gravity
• D. Balanced
Question 2
• Which kind of forces are exerted on an object
if there is a net force of zero?
• A. Unbalanced
• B. Kinetic friction
• C. Gravity
• D. Balanced
SPS8. Students will determine relationships
among force, mass, and motion.
• b. Apply Newton’s three laws to everyday
situations by explaining the following: 1)
Inertia 2) Relationship between force, mass
and acceleration 3) Equal and opposite forces
– Know real world examples
– If given a situation, be able to predict what will
happen
Question 3
• Which two forces operate to keep a moon in
orbit around a planet?
• A. Inertia and gravity
• B. Inertia and friction
• C. Friction and gravity
• D. Distance and gravity
Question 3
• Which two forces operate to keep a moon in
orbit around a planet?
• A. Inertia and gravity
• B. Inertia and friction
• C. Friction and gravity
• D. Distance and gravity
Question 4
• A baby pushes on a large chair. What is the
reaction force?
• A. Friction pushes on the chair
• B. Friction pushes on the baby
• C. The chair pushes on the baby
• D. The chair pushes on the floor
Question 4
• A baby pushes on a large chair. What is the
reaction force?
• A. Friction pushes on the chair
• B. Friction pushes on the baby
• C. The chair pushes on the baby
• D. The chair pushes on the floor
Question 5
• A student kicks a soccer ball across a field.
The ball rolls across the field and stops. What
causes the ball to stop?
• A. Gravity acts on it
• B. Its own inertia stops it
• C. Friction acts on it
• D. Balanced forces act on it
Question 5
• A student kicks a soccer ball across a field.
The ball rolls across the field and stops. What
causes the ball to stop?
• A. Gravity acts on it
• B. Its own inertia stops it
• C. Friction acts on it
• D. Balanced forces act on it
SPS8. Students will determine relationships
among force, mass, and motion.
• c. Relate falling objects to gravitational force
– Understand how objects accelerate due to gravity
– Understand that the gravitational attraction
between two objects depends on MASS and
DISTANCE
Question 6
• Suppose you roll a basketball and a baseball
toward each other. How does this affect the
force they exert on each other?
• A. It increases
• B. It decreases
• C. It stays the same
• D. It disappears
Question 6
• Suppose you roll a basketball and a baseball
toward each other. How does this affect the
force they exert on each other?
• A. It increases
• B. It decreases
• C. It stays the same
• D. It disappears
Question 7
• Which pair of objects will have the LEAST
gravitational attraction?
• A. Two cinder blocks 6 cm apart
• B. Two marbles 12 cm apart
• C. A cinder block and a marble 6 cm apart
• D. A cinder block and a marble 12 cm apart
Question 7
• Which pair of objects will have the LEAST
gravitational attraction?
• A. Two cinder blocks 6 cm apart
• B. Two marbles 12 cm apart
• C. A cinder block and a marble 6 cm apart
• D. A cinder block and a marble 12 cm apart
• Gravitational attraction depends on mass and
distance
SPS8. Students will determine relationships
among force, mass, and motion.
• d. Explain the difference in mass and weight.
– Know that weight changes if gravity changes, but
mass does not
Question 8
• Which statement is correct?
• A. Weight is the amount of material in an
object
• B. Mass is the physical dimensions of an
object
• C. Weight is the gravitational pull on an object
• D. Mass is the gravitational pull on an object
Question 8
• Which statement is correct?
• A. Weight is the amount of material in an
object
• B. Mass is the physical dimensions of an
object
• C. Weight is the gravitational pull on an
object
• D. Mass is the gravitational pull on an object
Question 9
• Your weight on Mars is only about 1/3 your
weight on Earth. Which reason BEST explains
this?
• A. Mars is more massive than Earth
• B. Mars has a smaller force of gravity than Earth
• C. Mars has a greater force of gravity than Earth
• D. An object on Mars has less mass than the
same object on Earth
Question 9
• Your weight on Mars is only about 1/3 your
weight on Earth. Which reason BEST explains
this?
• A. Mars is more massive than Earth
• B. Mars has a smaller force of gravity than Earth
• C. Mars has a greater force of gravity than Earth
• D. An object on Mars has less mass than the
same object on Earth
SPS8. Students will determine relationships
among force, mass, and motion.
• e. Calculate amounts of work and mechanical
advantage using simple machines.
– Know the six simple machines
– Understand how they help us do work
– Know how to calculate work and MA if given the
basic versions of the formula
– Know units of work, force, and distance
Six Simple Machines
• Inclined Plane
• Wedge
• Screw
• Lever
• Pulley
• Wheel & Axle
Mechanical Advantage
Inclined Plane
• Reduces force, but increases distance
• The mechanical advantage of an inclined
plane is length divided by height.
• Wedges and screws are types of inclined
planes.
MA = L/H
Wedge
• A wedge generates outward forces
• A wedge is a type of inclined plane. Its
mechanical advantage is its length divided by
its greatest thickness.
Screw
• A screw is an inclined
plane wrapped around
a cylinder
• Uses a small force over
a longer distance
• The closer the threads,
the lower the force
required
Levers – Three Classes
• Can change direction & size of force
• In a first-class lever, the fulcrum is between
the force and the load.
• In a second-class lever, the load is between
the force and the fulcrum.
• In a third-class lever, the force is between the
fulcrum and the load.
First Class Lever
Change direction & maybe force
Second Class Lever
Change force, but not direction
Third Class Lever
Don’t change direction, output < input
Pulleys
• Change direction and may change input force
• Types of pulleys include fixed pulleys, movable
pulleys, and block and tackles.
Wheel and Axle
• The mechanical advantage of a wheel and axle
is the radius of the wheel divided by the
radius of the axle.
Compound Machines
• Compound machines consist of two or more
simple machines.
• Compound machines have low mechanical
efficiencies because they have more moving
parts and therefore more friction to
overcome.
Question 1
• Which of the following simple machines is a
wedge?
• A. Wheelbarrow
• B. Doorknob
• C. Ax
• D. Truck ramp
Answer
• Which of the following simple machines is an
example of a wedge?
• A. Wheelbarrow
• B. Doorknob
• C. Ax
• D. Truck ramp
Question 2
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What is the pivot point of a lever called?
A. Load
B. Fulcrum
C. Wedge
D. Effort
Answer
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What is the pivot point of a lever called?
A. Load
B. Fulcrum
C. Wedge
D. Effort
Question 3
• A student pushes on a lever with a force of
40N. The 150N load does not move. Which of
the following is true?
• A. Input force is 40 N and work done is 0 J.
• B. Input force is 40 N and work done is 600 J.
• C. Output force is 40 N and work done is 150J.
• D. Output force is 150N and work done is 40J.
Answer
• A student pushes on a lever with a force of
40N. The 150N load does not move. Which of
the following is true?
• A. Input force is 40 N and work done is 0 J.
• B. Input force is 40 N and work done is 600 J.
• C. Output force is 40 N and work done is 150J.
• D. Output force is 150N and work done is 40J.