Order ID | 53563633773 |
Type | Essay |
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Perfect Number of Pages to Order | 5-10 Pages |
Drawing A FBD For the Falling Coffee Filter
Lab 2: Types of Forces
Experiment 2: Velocity and Air resistance in a vacuum, all objects accelerate due to gravity at the same rate: 9.8 m/s
2 . In actuality, fric on from
air resistance prevents this from happening. A falling object will accelerate un l the force of air re‐ sistance matches the force on it due to gravity (mg). When these forces are equal, the object is said to have reached terminal velocity, and will con nue to fall at a constant rate indefinitely. In this experiment you will see how the air resistance of an object can work against the force of gravity for an object of low weight and a large air resistance. If the object is light enough, air resistance can cancel out the force of gravity, resul ng in a constant velocity.
Procedure 1 1. Measure the height of a table and record the value in Table 2. 2. Push one coffee filter off the edge of the table and start the stopwatch. In Table 2, record how
long it takes for the filter to hit the ground in Table 2. Repeat four mes and average your results. 3. Using the average me calculated from Step 2, find the average speed of the falling filter using the
measured height of the table. 4. Repeat Steps 2‐3 with two coffee filters stuck together.
Procedure 2 1. Find a higher table, or get a friend to help you drop the filter from a higher spot. Measure the actu‐
al height. 2. Push one coffee filter off the edge of the table and start the stopwatch. In Table 2, record how
long it takes for the filter to hit the ground in Table 2. Repeat four mes and average your results in Table 2.
Using the average, me calculated from Step 2, find the average speed of the falling filter using the measured height of the table.
Repeat Steps 2‐3 with two coffee filters stuck together.
Materials Tape measure Stopwatch Coffee filters (re‐shape to how they would sit in a coffee pot)
36
Lab 2: Types of Forces
Please submit your table data and answers for this experiment on the Word document provided to you.
Ques ons 1. Draw a FBD for the falling coffee filter. What is the net force?
Table 2: Coffee Filter Data
Procedure 1
1 Coffee Filter 2 Coffee Filters
Height of table (m)
Total Time (s) ‐ Trial 1
Total Time (s) ‐ Trial 2
Total Time (s) ‐ Trial 3
Total Time (s) ‐ Trial 4
Total Time (s) ‐ Trial 5
Calculated average speed (m/s)
Procedure 2
Measured height (m)
Calculated average speed (m/s)
Total Time (s) ‐ Trial 5
Total Time (s) ‐ Trial 1
Total Time (s) ‐ Trial 4
Total Time (s) ‐ Trial 2
Total Time (s) ‐ Trial 3
37
Lab 2: Types of Forces
What are we assuming by using the average velocity from Procedure 1 to es mate the height of the fall in Procedure 2?
Draw the FBD for the 2‐filter combina on, assuming constant velocity. What is the net force?
How do your measured and calculated values for the height in Procedure 2 compare? If they are significantly different, explain what you think caused the difference.
Why do two coffee filters reach a higher velocity in free fall than one coffee filter?
How would the FBD differ for a round rubber ball dropped from the same height?
Lab 3: Newton’s Laws
41
Lab 3: Newton’s Laws
Forces can produce or prevent mo on. The laws used today to describe all aspects of mo on date back to the 1700s, when Sir Isaac Newton proposed a set of rules to describe how all objects move. New‐ ton’s First Law of Mo on states that an object will remain at rest, or in uniform mo on, unless acted on by an unbalanced force. In other words, objects have the tendency to resist changes in mo on. The concept that force can change the velocity of a mass is very important. Nothing would change without forces. Newton’s First Law is also called the Law of Iner a. Iner a is an object’s tendency to resist changes in state of mo on (speed or direc on). Ma er has this property whether it is at rest or in mo on. The First Law states that an object will con nue at a constant velocity in one direc on unless acted on by a net force. When a net force on an object is applied, the object will accelerate in the direc on of that
Figure 1: Newton’s First Law of Mo on in ac onbilliard balls remain at rest un l an external force (the cue ball) causes them to move.
Concepts to explore: · Newton’s First Law
42
Lab 3: Newton’s Laws
force. The movement of planets around the Sun is an example of in‐ er a. Planets have a lot of mass, and therefore a great amount of iner a—it takes a huge force to accelerate a planet in a new direc‐ on. The pull of gravity from the Sun keeps the planets in orbit—if
the Sun were to suddenly disappear, the planets would con nue at a constant speed in a straight line, shoo ng off into space! Newton also observed a special rela onship between mass and iner‐ a. Mass is o en confused with weight, but the difference is crucial in
physics. While mass is the measure of how much ma er is in an ob‐ ject (how much stuff is there), weight is a measure of the force expe‐ rienced by an object due to gravity. Thus, weight is rela ve to your loca on – your weight would differ at the Earth’s core, at the summit of Mount Everest, and especially in outer space, when compared to the surface. On the other hand, mass remains constant in all these loca ons. Mathema cally, weight is the mass of an object mul plied by its accelera on due to gravity:
w = mg
where w is weight, m is mass and g is gravity. Sir Isaac Newton noted that the greater an object’s mass, the more it resisted changes in mo on. Therefore, he concluded that mass and iner a are directly propor onal (↑mass = ↑iner a). This predic on produced Newton’s Second Law of Mo on, an expression for how an object will accelerate based on its mass and the net force applied to the object. This law can be summarized by the equa on:
ΣF = ma where ΣF is the sum of all force’s ac ng on the object, m is its mass and a is its accelera on. The stand‐ ard measurement for mass is the kilogram (kg), and for accelera on is the meter/sec/sec, or m/s
2 . The
standard measurement for force is the Newton, where 1 N = 1 kg·m/s 2 . Comparing this equa on to the
first one helps reinforce the difference between mass and force (such as weight). Newton’s Third Law of Mo on states that for every ac on there is an equal, but opposite reac on. When you hold up a heavy object, the force of gravity is pulling the object down against your hands. In order to keep the object from falling to the floor, your hands and arms supply an equal and opposite force upward against the ball. Thus, single forces do not exist, only pairs of forces (the ac on force and the reac on force). You might not think about it, but you do not directly feel the force of gravity when you stand on the ground; what you’re really feeling is the opposing force exerted by the ground that keeps you from falling toward the center of the earth! Even when you walk, you push against the ground, and it pushes right back! Newton’s three laws of mo on govern the rela onship of forces and accelera on. There are many ap‐ plica ons of Newton’s Laws in your everyday life. To get that last bit of ketchup from the bo le, you
Figure 2: When this player leaps to the bas‐ ket you are seeing the Third Law in ac on: the player’s downward push receives an equal and opposite force upward from the ground. Without this reac on force, he
would have no way to accelerate upward to the rim.
43
Lab 3: Newton’s Laws
shake the bo le upside‐down, and quickly stop it (with the lid). Consider riding in a car. Have you ever experienced iner a while rapidly accelera ng or decelera ng? Thousands of lives are saved every year by seatbelts, which are safety restraints that protect against the iner a that propels a person forward when a car comes to a quick stop.
Experiment 1: Newton’s First Law
Procedure 1. Fill the container with about 4 inches of water. 2. Find an open space outside to walk around in with the container of water in your hands. 3. Perform the following ac vi es:
Start with the water at rest (i.e., on top of a table). Grab the container and quickly acceler‐ ate.
Walk with constant speed in a straight line for 15 feet. c. A er walking a straight line at constant speed, make an abrupt right‐hand turn. Repeat with
a le ‐hand turn. d. A er walking a straight line at constant speed, stop abruptly.
Record your observa ons for each type of mo on from Step 3 in the space below. Comment on where the water tended to move. If it spilled, note if it spilled right, le , away from you, or toward you.
Materials Deep bowl or pitcher* Water* * You must provide
44
Lab 3: Newton’s Laws
Ques ons Please submit your answers for this experiment on the Word document provided to you.
Explain how your observa ons of the water demonstrate Newton’s law of iner a.
Draw a free body diagram of your containers of water from the situa on in Step 3, Part d. Draw arrows for the force of gravity, the normal force (your hand pushing up on the container), and the stopping force (your hand decelera ng the container as you stop.) What is the direc on of the water’s accelera on?
*Note, free body diagrams are discussed in depth in Lab 2: Types of Forces. See Figure 3 for a sample diagram. Remember, the ob‐ ject is usually indicated as a box, and each force that acts upon the box is indicated with an arrow. The size of the arrow indicates the magnitude of the force, and the direc on of the arrow indi‐ cates the direc on which the force is ac ng. Each arrow should be labeled to iden fy the type of force. Note, not all objects have four forces ac ng upon them.
Can you think of any instances when your are driving or riding a car that are similar to this experi‐ ment? Describe two instances where you feel forces in a car in terms of iner a.
Experiment 2: Unbalanced Forces – Newton’s Second Law This experiment will demonstrate the mechanical laws of mo on using a simple assembly similar to that used by Rev. George Atwood in 1784 to verify Newton’s Second Law, named the Atwood machine.
Materials Pulley String Tape Measure Stop watch 2 Paperclips 15 Washers Masking tape
Ffric on Fapp
Fnormal
Fgravity
Figure 3
45
Lab 3: Newton’s Laws
Procedure 1 1. Support the pulley so that objects hanging from it can descend
to the floor. (i.e., Tape a pencil to the top of a table, door, etc.) Remember that higher support will produce longer me inter‐ vals which are easier to measure. See
Thread a piece of string through the pulley so that you can a ach washers to both ends of the string. The string should be long enough for one set of washers to touch the ground with the other set near the pulley. (You may a ach the washers using a paperclip or by tying them on.)
Count out 15 washers 4. A ach seven washers to each end of the string. 5. Observe how the washers on one side behave when you pull
on the washers on the other side. Answer ques on 1 based on your observa ons.
Add the remaining washer to one end of the string so one side of the string has seven washers (M1), and the other has 8 washers a ached to it (M2).
Place M1 on the floor. Measure the height of M2 when sus‐ pended while M1 is on the floor. Measure the distance M2 falls when you release the light set when it is in contact with the floor, and record it in Table 1.
Time how long it takes for M2 to reach the floor. 9. Repeat Steps 7 ‐ 8 four more mes (for a total of five mes),
recording the values in Table 1. Calculate the average me. 10. Calculate the accelera on (assuming it is constant) from the
average me and the distance the washers moved. Refer to the “Hint” below Table 1 for help.
Procedure 2 1. Transfer one washer, so that there are six on one end of the
string (M1) and nine on the other (M2). 2. Place the M1 on the floor. Measure the height that M2 is sus‐
pended at while M1 is on the floor. Measure the distance M2 will fall if you release the light set when it is in contact with the floor.
Time how long it takes for the heavy set of washers to reach the floor.
Repeat Steps 2 ‐ 3 four more mes (for a total of five mes), recording the values in a table and then calculate the average me.
Calculate the accelera on (assuming it is constant) from the average me and the distance the washers moved.
Figure 5: Atwood machine. The tension force is directed up for both M1 and M2. M1 accelerates upward, and M2 acceler‐ ates downward. Do you know what causes the downward force?
M2
M1 Tension force
Tension force
Figure 4: Sample experimental set‐up. This set‐up hangs the pulley from a pencil that has been taped to a table. Although, any level surface (such as a counter‐top or door) will suffice. Metal washers will also be ed to both ends of the string for this experiment. Do not e the string in a knot you cannot un e!
46
Lab 3: Newton’s Laws
Please submit the table data and answers for this experiment on the Word document provided to you. Table 1: Mo on Data for Experiment 2
Trial M1 M2 Δd of M2 Time (s) Accelera on
Procedure 1
1
2
3
4
5
Average
Procedure 2
1
2
3
4
5
Average
Hint: You need to rearrange the formula d = 1/2 at 2 to calculate the accelera on. In this equa on,
d = distance, a = accelera on, and t = me.
Example: Suppose you set up an Atwood Machine. The M2 weight accelerates downward a distance of 1.30 me‐ ters in 1.50 seconds. What was the accelera on rate? Given: d = 1.30 meters t = 1.50 seconds The goal is to rearrange the formula to end with “a” by itself on one side of the equa on. To do this… 1. Set up your equa on, and square the value for t; 1.30 meters =
1 /2 · (a · (1.50 seconds)
2 )
Remove the “ 1 /2” by mul plying each side of the equa on by 2;
47
Lab 3: Newton’s Laws
Ques ons 1. When you give one set of washers a downward push, does it move as easily as the other set? Does
it stop before it reaches the floor. How do you explain this behavior?
Draw a FBD for M1 and M2 in each procedure (Procedure 1 and Procedure 2). Draw force arrows for
the force due to gravity ac ng on both masses (Fg1 and Fg2) and the force of tension (FT). Also draw
arrows indica on the direc on of accelera on, a.
Experiment 3: Newton’s Third Law
Procedure 1. Tie one end of the fishing line to a chair. Space the second chair about 10 feet away. 2. String the other end of the fishing line through the straw. 3. Tie the loose end of the fishing line to the second chair. 4. Inflate a balloon. Hold it closed with your fingers, and tape it to the straw. 5. Slide the straw/balloon back so that the mouth of the balloon is facing the nearest chair. 6. Let go of the balloon and observe what happens.
Materials Fishing line Balloon Plas c straw Masking tape 2 Chairs* *You must provide
48
Lab 3: Newton’s Laws
Ques ons Please submit your answers for this experiment on the Word document provided to you.
Explain what caused the balloon to move in terms of Newton’s Third Law.
What is the force pair in this experiment? Draw a Free Body Diagram (FBD) to represent the (unbalanced) forces on the balloon/straw combina on.
Add some mass to the straw by taping some metal washers to the bo om and repeat the experi‐ ment. How does this change the mo on of the assembly? How does this change the FBD?
If the recoil of the rifle has the same magnitude force on the shooter as rifle has on the bullet, why does the shooter not fly backwards with a high velocity?
Lab 4: Acids & Bases
51
Lab 4: Acids & Bases
Introduc on
Have you ever had a drink of orange juice a er brushing your teeth?
What do you taste when you brush your teeth and drink orange juice a erwards? Yuck! It leaves a really bad taste in your mouth. But why? Orange juice and toothpaste by them‐ selves taste good. The terrible taste is the result of an acid/base reac on that occurs in your mouth. Orange juice is a weak acid and the toothpaste is a weak base. When they are placed together, they neutralize each other and produce a product that is unpleasant to taste. In this lab we will discover how to dis nguish between acids and bases.
Two very important classes of compounds are acids and bases. But what exactly makes them different? Acids and bases have physical and chemical differences that you can ob‐ serve and test. According to the Arrhenius defini on, acids ionize in water to produce a hydronium ion (H3O
+ ), and bases dissociate in water to produce hydroxide ion (OH
‐ ).
Physical differences between acids and bases can be detected by the senses, including taste and touch. Acids have a sour or tart taste and can produce a s nging sensa on to broken skin. For example, if you have ever tasted a lemon, it can o en result in a sour face. Bases have a bi er taste and a slippery feel. Soap and many cleaning products are bases. Have you accidentally tasted soap or had it slip out of your hands?
Reac ons with acids and bases vary depending on the par cular reactants, and acids and bases each react differently with other substances. For example, bases do not react with most metals, but acids will react readily with certain metals to pro‐ duce hydrogen gas and an ionic compound—which is referred to as a salt. An example of this type of reac on occurs when magnesium metal reacts with hydrochloric acid. In this reac on, magnesium chloride (a salt) and hydrogen gas are formed.
Mg (s) + 2 HCl (aq) → MgCl2 (aq) + H2(g)
metal + acid → a salt + hydrogen gas
Acids may also react with a carbonate or bicarbonate to form carbon dioxide gas and water. The general reac on equa on for a reac on between an acid and a carbonate can be represented in this manner:
CO3 2-
(aq) + 2 H3O +
(aq) → CO2 (g) + 3 H2O (l)
carbonate + acid → carbon dioxide + water
The general equa on for a reac on between an acid and a bicarbonate is similar and can be represented in this manner:
Figure 1: Orange juice has a pH of around 3.5. Dairy milk, by comparison, is much less acid‐ ic, with a pH of around 6.5.
Concepts to explore: · Understand the proper es and reac ons of acids and bases · Relate these proper eses to common household products
52
Lab 4: Acids & Bases
HCO3 –
(aq) + H3O +
(aq) → CO2 (g) + 2 H2O (l)
Acids and bases can also react with each other. In this case, the two opposites cancel each other out so that the product formed has neither acidic nor basic (also called alkaline) proper es. This type of reac on is called a neutraliza on reac on. The general equa on for the reac on between an acid and a base is represented in this manner:
H3O + + OH – → 2 H2O
An example of a neutraliza on reac on is when an aqueous solu on of HCl, a strong acid, is mixed with an aqueous solu on of NaOH, a strong base. HCl, when dissolved in water, forms H3O
+ and Cl
‐ .
NaOH in water forms Na
+ and OH
‐ . When
the two solu ons are mixed together the products are water and common table salt (NaCl). Neither water nor table salt has acid or base proper es. Generally, this reac on is wri en without the water solvent shown as a reactant:
HCl + NaOH → H2O + NaCl
There is another group of acids called organic acids. Ace c acid found in vinegar and citric acid found in citrus fruit are examples of organic acids. These acids are all much weaker than HCl. Organic acids have at least one –CO2H group in their molecular formula. When a base is added, the –H of the –CO2H group is replaced just like the –H in HCl. In this lab you will use citric acid as the acid and sodium bicarbonate as the base. Citric acid has three –CO2H groups and only each of the H’s on these groups react with a sodium bicarbonate. The other H’s in the formula do not react. This reac on can be represented in this manner:
HOC(CO2H)(CH2CO2H)2 + 3 NaHCO3 → HOC(CO2 ‐ Na
+ )(CH2CO2
‐ Na
+ )2 + 3 CO2 + 3 H2O
Acids and bases are measured on a scale called pH. The pH of a substance is defined as the nega ve log of its hydronium ion concentra on. An aqueous (water) solu on that has a lot of hydronium ions but very few hy‐ droxide ions is considered to be very acidic, while a solu on that contains many hydroxide ions but very few hydronium ions are considered to be very basic.
pH = ‐ log [H3O + ]
pH values range from less than 1 to 14, and are measured on a logarithmic scale (equa on above). This means that a substance with a pH of 2 is 10‐ mes (10
1 ) more acidic than a substance with a pH of 3. Similarly, a pH of
7 is 100‐ mes (10 2 )more basic than a pH of 5. This scale lets us quickly tell if something is very acidic, a li le
bicarbonate + acid → carbon dioxide + water
Table 1: Approximate pH of various common foods.
Food pH Range
Lime 1.8 ‐ 2.0
So Drinks 2.0 ‐ 4.0
Apple 3.3 ‐ 3.9
Tomato 4.3 ‐ 4.9
Cheese 4.8 ‐ 6.4
Potato 5.6 ‐ 6.0
Drinking Water 6.5 ‐ 8.0
Tea 7.2
Eggs 7.6 ‐ 8.0
Acid + Base → Water
53
Lab 4: Acids & Bases
acidic, neutral (neither acidic nor basic), a li le basic, or very basic. A pH of 1 is highly acidic, a pH of 14 is highly basic, and a pH of 7 is neutral.
pH indicators, which change color under a certain pH level, can be used to determine whether a solu on is acidic or basic. Litmus paper is made by coa ng a piece of paper with litmus, which changes color at around a pH of 7. Either red or blue litmus paper can be purchased depending on the experimental needs. Blue lit‐ mus paper remains blue when dipped in a base, but turns red when dipped in an acid, while red litmus paper stays red when dipped in an acid, but turns blue when in contact with a base.
A more precise way to determine acidity or basicity is with pH paper. When a substance is placed on pH pa‐ per a color appears, and this color can be matched to a color chart that shows a wide range of pH value. In this way, pH paper allows us to determine to what degree a substance is acidic or basic and can provide an approximate pH value.
Pre‐lab Ques ons
What is a neutraliza on reac on?
Hydrochloric acid (HCl) is a strong acid. About what pH would you expect it to be?
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