Download Measurement and Force

Midterm Review
Measurement and Force
• Tools
• Graduated Cylinder
• Triple Beam Balance
Measure
Volume
Mass
Measuring Volume
We will be using graduated cylinders to
find the volume of liquids and other objects.
Read the measurement based on the bottom of the
meniscus or curve. When using a real cylinder, make
sure you are eye-level with the level of the water.
What is the volume of water in the cylinder? _____mL
What causes the meniscus?
A concave meniscus occurs when the molecules of the liquid
attract those of the container. The glass attracts the water on
the sides.
Top Image: http://www.tea.state.tx.us/student.assessment/resources/online/2006/grade8/science/images/20graphicaa.gif
Bottom Image: http://morrisonlabs.com/meniscus.htm
What is the volume of water in each cylinder?
Pay attention to the scales for each cylinder.
Images created at http://www.standards.dfes.gov.uk/primaryframework/downloads/SWF/measuring_cylinder.swf
Measuring Liquid Volume
Measuring Solid Volume
9 cm
We can measure the volume of regular object
using the formula length x width x height.
8 cm
_____ X _____ X _____ = _____
We can measure the volume of
irregular object using water displacement.
Amount of H2O with object = ______
About of H2O without object = ______
Difference = Volume = ______
Click here for an online activity about volume.
Choose Lessons  Volume & Displacement
http://resources.edb.gov.hk/~s1sci/R_S1Science/sp/e
n/syllabus/unit14/new/testingmain1.htm
10 cm
Determine The Mass
Problem/Question
Observation/Research
Formulate a Hypothesis
Experiment
Collect and Analyze Results
Conclusion
Every Good Experiment has Three
Variables
• Independent
(Manipulated)
– This is the variable
the scientist changes
• Dependent
(Responding)
– This is the variable
that changes
because of what the
scientist did
• Controlled Variable – a variable that is
not changed
– Also called constants
– Allow for a “fair test”
Force and Motion
- The Nature of Force
Combining Forces
(Real World Examples + Tug-of-War Challenge)
•Do forces usually act alone? The combination of all forces acting on an object is called the net
force.
- The Nature of Force
Unbalanced Forces
•Unbalanced forces acting on an object result in
a net force and cause a change in the object’s
motion.
- The Nature of Force
Balanced Forces
•Balanced forces acting on an object do not change the object’s motion.
A force is…
A. Always balanced.
B. A push or a pull.
C. A pull that pushes.
D. What Jedi Knights possess.
A force is measured by its
A. Power only.
B. Strength or magnitude only.
C. Strength or magnitude and direction.
D. Direction and its pull.
A sky diver experiences a 900 N downward force and a 200 N
upward force. What is the net force (in the correct direction)?
A.
B.
C.
D.
700 N up
700 N down
1100 N up
1100 N down
Which direction will the cart below
move?
A.
B.
C.
D.
The cart will not because the forces are balanced.
Left because the net force is -90 N to the left.
Right because the net force is 90 N to the right.
Up because the cart is being pulled to the left and to
the right.
The two dogs in the picture below are pulling on a rope. The dog
on the left is pulling at 200 N while the dog on the right is pulling
at 200 N. What direction will the rope move?
A.
B.
C.
D.
South because the forces are balanced.
West because the dog on the left is pulling harder.
East because the dog on the right is stronger.
The rope will not move because the forces are balanced.
Friction Notes
•Friction is a force that resists or inhibits the motion of
objects when they move against each other.
•Also, you should know that the type of surface of an
object and that how hard surfaces push together
affect friction (you increased the 2nd variable in bold
by adding more weight).
•Lastly, know how wheels affect friction as well as any
other ways to reduce friction.
Markie and Suzy are moving a safe across the floor. Which of the
following describes the frictional force?
A.
B.
C.
D.
Markie and Suzy both push the safe the same direction.
The weight of the safe exerts a downward force.
The floor pushes upward on the safe.
There is some resistance going against the direction the
safe is moving.
Which change would require more force to pull the wooden block
up the ramp?
A. Glue sandpaper to the surface of the ramp.
B. Reduce the mass of the wooden block.
C. Restack the books so the thinnest book is on the bottom.
D. Have the student use two hands.
Which of the following would produce the greatest frictional force
between 2 objects?
A.
B.
C.
D.
A 100 kg wooden block sliding across a smooth table.
A 200 kg wooden block sliding across a smooth table.
A 100 kg wooden block sliding across a rug.
A 200 kg wooden block sliding across a rug.
The diagrams below show a person
moving a 50-kilogram object up a
ramp. In which diagram is there the
least amount of friction on the object?
A.
B.
C.
D.
Diagram 1
Diagram 2
Diagram 3
Diagram 4
The wheels and gears of machines are greased in order to
decrease
A.
B.
C.
D.
Potential energy.
Output.
Efficiency.
Friction.
- Friction and Gravity
Gravity
•The force of gravity on a person or object at the surface of a planet is known as
weight.
•Right now you are experiencing 1G, which is the amount of force due to the
gravity on Earth.
•When you ride on a rollercoaster, you will experience more than 1G.
Sometimes, you are feeling 3, 4, or 5 G’s due to the acceleration of the
rollercoaster.
Gravitational Pull Experiment- Part 2:
Mass & Gravitational Pull of the Planets
•Name
Mass (X 1024 kg)
Gravitational force on the surface
(relative to Earth)
0.1
•Pluto
0.0013
•Moon
•
•Mars
•
•Earth
0.07
0.2
0.64
0.4
5.98
1.0
1900
2.4
1,989,000
7.1
•Jupiter
•
•Sun
•Conclusion: So, what else affects the gravitational pull between 2 objects?
- Friction and Gravity
Gravity
•Two factors affect the gravitational attraction between objects: mass and
distance.
Which two factors determine the gravitational attraction between
two objects?
A. time and temperature
B. shape and orbital speed
C. color and hardness
D. mass and distance apart
The gravitational force between the Moon and Earth depends on
A.
B.
C.
D.
Their masses only.
Their diameters only.
Their masses and how far apart they are.
Their diameters and how far apart they are.
Suppose three new planetary bodies are discovered near Earth.
They all have the same mass. Planet A is 9 million miles away,
Planet B is 7 million miles away, and Planet C is 30 million miles
away. Which planet would Earth have the greatest gravitational
attraction for?
A.
B.
C.
D.
Planet A
Planet B
Planet C
Planet D
On which planet in our solar system would you feel the most
gravitational pull?
A.
B.
C.
D.
Earth
Saturn
Jupiter
Mars
Name
Mass (X 1024 kg)
Earth
Mars
Jupiter
Pluto
Moon
Sun
5.98
0.64
1900
0.0013
0.07
1,989,000
Gravitational force on the surface
(relative to Earth)
1.0
0.4
2.4
0.1
0.2
7.1
Why does the Sun have the greatest gravitational pull?
A.
B.
C.
D.
It has the lowest mass.
It has the most mass.
It’s the closest to the Earth.
It’s gravitational force is 7.1 times that of Earth.
Name
Mass (X 1024 kg)
Earth
Mars
Jupiter
Pluto
Moon
Sun
5.98
0.64
1900
0.0013
0.07
1,989,000
Gravitational force on the surface
(relative to Earth)
1.0
0.4
2.4
0.1
0.2
7.1
- Friction and Gravity
Free Fall
•Calculating:
–Calculate the slope of the
graph. What does the slope
tell you about the object’s
motion?
–The slope is 9.8. The speed
increases by 9.8 m/s each
second. This is the actual
acceleration due to gravity
on Earth without any air
resistance.
- Friction and Gravity
Air Resistance
•Falling objects with a greater surface area experience more air resistance.
Introduction to Newton’s 1st Law
•What happens to your body when a car or rollercoaster
first takes off quickly?
•What happens to your body when a car or rollercoaster stops abruptly?
st Law of Motion
Newton’s
1
•Objects in Motion (Pencil on a cart being stopped):
•Stay in motion until a force stops them from moving.
•Objects at Rest (Tablecloth Demo):
•Stay at rest until an outside force causes the object to move.
•Inertia:
•The tendency of an object to stay in motion or stay at rest.
•What does inertia depend on? Example- Which has more inertia
a toy car or a large truck?
•As mass increases, inertia increases.
•Newton’s 1st Law:
•An object in motion will stay in motion unless acted on by an
unbalanced force. Also, an object at rest will remain at rest unless
acted on by an unbalanced force.
Why is it difficult to stop a large fast-moving football player?
A. He has a small inertia.
B. An object at rest will stay at rest until an
unbalanced force causes it to move.
C. An object in motion will stay in motion until an
unbalanced force acts on it.
D. Because he plays for Notre Dame.
Why is it difficult to move heavy objects from rest?
A. Because they are at rest.
B. An object at rest tends to remain at rest until
an unbalanced force acts on it.
C. An object in motion will remain in motion
until an unbalanced force acts on it.
D. Because it’s light in weight.
The tendency of an object to remain at rest or remain in motion is
called ___________
A.
B.
C.
D.
Mass.
Inertia.
Newton’s 1st Law.
Density.
A.
B.
C.
D.
Which of the following affects the amount of inertia an object
possesses?
Mass
Volume
Gravity
Friction
Which of the following has the most
inertia?
A. A table
B. Grandma
C. A Toyota Yaris
D. A freight train
What Affects Force? (Newton’s 2nd
Law)
1.
Suppose you push two people who have the same mass. You push with more force on one person
vs. the other. Which person would accelerate faster from rest?
2.
Suppose you push two people and they both accelerate at the same rate. However, one person has
much more mass than the other. Which one required more force to accelerate?
3.
Suppose you push two people with the same amount of force. However, one person has more
mass than the other. Which person would accelerate at a faster rate?
F=mxa
Acceleration due to gravity & Constant force
•Force, mass, and acceleration units:
•1 N = 1 kg x m/s/s
a=
=
Acc.
Due to
Gravity
Which of the following best describes the relationships between
force, mass, and acceleration?
A. As mass decreases, the net force will increase if the
acceleration remains constant.
B. As mass and acceleration increase together, so will
the net force.
C. As mass increases so will the acceleration, but
force will remain constant.
D. As acceleration increases and the mass remains
constant, the net force will decrease.
Suppose you are pushing a car with a certain amount of force.
What will happen to the car’s acceleration if the mass of the car
increases? Assume the amount of applied force remains the
same.
A.
B.
C.
D.
The acceleration will increase.
The acceleration will decrease.
The acceleration will remain the same.
There is not enough information from the problem.
Newton’s 3rd Law
•Balloon Race Activity: Determine what makes
the balloon propel across the room based upon
the forces involved.
•Newton’s 3rd Law:
•For every action, there is an equal and
opposite reaction.
•What are the action-reaction forces for the
following:
–Rocket taking off?
–Punching a wall?
–Jumping from a high height to the ground?
– Hammering a nail?
Which of the following is an example of Newton’s 3rd Law of
Motion?
A. When you do push-ups, you won’t stop until an
unbalanced force causes you to stop.
B. The net force you exert when doing a push-up is
equal to your body mass multiplied by the
acceleration due to gravity.
C. When you do a push-up, an equal and opposite
force pushes back on your body or hands.
D. What’s a push-up?
What direction will the contraption shown below go when the
string is burned?
A.
B.
C.
D.
left
right
up
down
Why will the contraption below move to the right?
A. Friction is going to the left
B. The rubber band snaps to the left, so the equal and opposite reaction
is for the wooden platform to move to the right.
C. Gravity pulls the wooden platform to the right when the rubber band
snaps.
D. The pencils cause the wooden platform to move to the right because
friction acts in the opposite direction.
If you add mass to the wooden platform, what effect would that
have on the distance it travels?
A.
B.
C.
D.
The distance would increase.
The distance would decrease.
The distance would not change.
It would travel the same distance in the opposite
direction.