how did Simard conduct her experiments

Answers

Answer 1

Answer:

Simard planted paper birch, fir, and cedar trees in a plot and then injected them with different radioactive isotope carbon dioxide gases and covered them with bags. She waited an hour, then checked the trees for radiation.


Related Questions

What mass of iron is produced from adding 80.0 g of iron(II) oxide (71.85 g/mol) to 20.0 g of magnesium metal? FeO (l) + Mg (l) ----------> Fe (l) + MgO (s) Identify the limiting reactant, mass of iron produced and the mass in grams of the excess reactant used in this reaction. Remember to report the correct number of significant figures and units where appropriate. You need to show work in order to receive credit. Zero points will be awarded if logical work/explanation is not given. You must show your work by typing it into the provided test box. I will not look to your scratch paper for work.

Answers

Answer:

46.0g of Iron are produced

Explanation:

Based on the chemical reaction:

FeO(l) + Mg(l) → Fe(l) + MgO(s)

1 mole of Iron (II) oxide reacts per mole of Mg to produce 1 mole of iron

To solve this question we need to convert each mass of reactant to moles using its respectives molar masses in order to find limitng reactant. Moles of limiting reactant = Moles of iron produced:

Moles FeO (Molar mass: 71.85g/mol):

80.0g * (1mol / 71.85g) = 1.11moles FeO

Moles Mg (Molar mass: 24.305g/mol)

20.0g * (1mol / 24.305g) = 0.823 moles Mg

As moles of Mg < Moles FeO, Mg is limiting reactant and the moles of Fe are 0.823 moles.

The mass of Iron produced is:

0.823 moles Fe * (55.845g/mol) =

46.0g of Iron are produced

Given the atomic mass of select elements, calculate the molar mass of each salt.

Element Molar mass
(g/mol)
Beryllium (Be) 9.012
Magnesium (Mg) 24.31
Cobalt (Co) 58.93
Cadmium (Cd) 112.41
Bromine (Br) 79.90
Match the numbers to the appropriate blanks in the sentences below. Make certain each sentence is complete before submitting your answer.
View Available Hint(s)
ResetHelp
1. The molar mass of MgBr2 is The molar mass of M g B r 2 is blank..
2. The molar mass of BeBr2 is The molar mass of B e B r 2 is blank..
3. The molar mass of CoBr2 is The molar mass of C o B r 2 is blank..
4. The molar mass of CdBr2 is The molar mass of C d B r 2 is blank..

Answers

1. 184.11
2. 168.812
3. 218.13
4. 272.21

study the image wich shows an air mass moving into a region wich type of weather will this region most likely experience due to the incoming air mass

Answers

Answer:

766ijn

Explanation:

hovibibbunununububububyhybyybybnu


help asap pls,
find the percent composition

Answers

Explanation:

1. Pb(CO3)2

Element Number Mass Percet Composition

Oxygen 6 16.00 29.34%

Carbon 2 12.01 7.34%

Lead 1 207.21 63.32%

2. Ga(OH)3

Element Number Mass Percet Composition

Hydrogen 3 1.0079 2.50%

Oxygen. 3 16.00 39.75%

Gallium 1 69.72 57.74%

3. P4O10

Element Number Mass Percet Composition

Oxygen. 10 16.00. 56.36%

Phosphorus. 4 30.97 43.64%

4. Ca3P2

Element Number Mass Percet Composition

Phosphorus 2 30.97 34.00%

Calcium. 3 40.08 66.00%

5. Ti(NO3)3

Element Number Mass Percet Composition

Oxygen. 9 16.00 61.56%

Titanium. 1 47.87 20.47%

Nitrogen. 3 14.01 17.97%

An airplane has a mass of 12,000kg. If it is accelerating at 16m/sec2, what is its force?(round to the nearest whole number) NEED THIS ASAP

Answers

Answer:

[tex]F=1.92x10^5N[/tex]

Explanation:

Hello!

In this case, since the force exerted by an object with a certain mass an acceleration is:

[tex]F=m*a[/tex]

We can plug in the given mass of 12,000 kg and acceleration of 16 m/s^2 to obtain:

[tex]F=12,000kg*16m/s^2\\\\F=192,000kg*m/s^2\\\\F=1.92x10^5N[/tex]

Best regards!

Zn(s) + 2 HCl(aq) —> ZnCl2(aq)
+ H2(g)
If a scientist wanted to create 10L of hydrogen gas at RTP, what mass of HCl would they need to start with?

Answers

Answer:

First write the balanced equation for the reaction of HCl with Zn (NOTE: the previous answer did NOT do this and thus obtained an incorrect answer)

Zn + 2HCl ==> ZnCl2 + H2(g)

moles of H2 desired:  PV = nRT

n = PV/RT = (1 atm)(10L)/(0.0821 Latm/Kmol)(298K)

n = 0.409 mole H2 desired

moles Zn needed:

0.409 moles H2 x 1 mole Zn/2 moles HCl = 0.204 moles Zn needed

mass Zn needed = 0.204 moles Zn x 65.4 g/mol = 13.4 g Zn needed (to 3 sig. figs.)

Explanation:people always get this wrong but i got you

For the balanced equation shown below, what would be the limiting reagent if 42.3 grams
of N2O5 were reacted with 9.18 grams of H2O?
N2O5+H2O---> 2HNO3

A. HNO3
B. H20
C. N205

Answers

Answer: A. HNO3

Explanation:

Which of the following particles has the smallest
mass?
A) electron
C) neutron
B) hydrogen atom
D) proton

Answers

Answer:

AN ELECTRON HAS THE SMALLEST MASS!

Answer:

A) electron

good luck, i hope this helps :)

(b) Why must acidic gases be treated before they are released into the atmosphere?

Answers

Answer:

because they react with other gases of atmosphere and pollute the environment

Determine the molecular formula for a compound that has a molecular mass of 52.0 g/mole
and and is composed of 92.31% carbon and 7.69% hydrogen.

Answers

Answer:

C4H4

Explanation:

92.31% of 52.0 g/mol is 48.0012 g/mol

7.69% of 52.0 g/mol is is 3.9988 g/mol

Carbon has a gram-formula mass of about 12, which goes into 48.0012 about 4 times, so there should be 4 atoms of Carbon

Hydrogen has a gram-formula mass of about 1, which goes into 3.9988 about 4 times, so there should also be 4 atoms of hydrogen

compound composed of cations and anions the forces of attraction that bind oppositely charged ions together lowest whole-number ratio of ions in an ionic compound a depiction of the valence electrons as dots around the symbol for an element a mixture of two or more elements, at least one of which is a metal the attraction of the free-floating valence electrons for the positively charged metal ions ions of the halogen atoms the electron(s) in the highest occupied energy level of an atom the number of ions of opposite charge that surround each ion in a crystal Atoms in a compound tend to have the electron configuration of a noble gas. Shows the kinds and numbers of atoms in the smallest representative unit of a substance a. halide ions b. alloy c. octet rule d. formula unit e. electron dot structure f. ionic compound g. ionic bonds h. coordination number i. chemical formula j. valence electrons k. metallic bond

Answers

Answer:

compound composed of cations and anions the forces of attraction that bind oppositely charged ions together - ionic compound

lowest whole-number ratio of ions in an ionic compound - formula unit

a depiction of the valence electrons as dots around the symbol for an element - electron dot structure

a mixture of two or more elements, at least one of which is a metal - alloy

the attraction of the free-floating valence electrons for the positively charged metal - metallic bond

ions of the halogen atoms - halide ions

the electron(s) in the highest occupied energy level of an atom - valence electrons

the number of ions of opposite charge that surround each ion in a crystal - coordination number

Atoms in a compound tend to have the electron configuration of a noble gas - octet rule

Shows the kinds and numbers of atoms in the smallest representative unit - chemical formula

Explanation:

An ionic compound is composed of oppositely charged ions held together in a crystal lattice. The lowest whole-number ratio of ions in an ionic compound is known as the formula unit.  The number of ions of opposite charge that surround each ion in a crystal is called the coordination number. Ions of the halogen atoms  are negatively charged and are called halide ions

Elements are composed of atoms, the electron(s) in the highest occupied energy level of an atom are called valence electrons. In metals, the attraction of the free-floating valence electrons for the positively charged metal is called the metallic bond. For atoms of elements, a depiction of the valence electrons as dots around the symbol for an element is called the electron dot structure or Lewis structure.

A combination of elements may be a compound or an alloy. An alloy usually contains at least one metal. For compounds, the chemical formula Shows the kinds and numbers of atoms in the smallest representative unit. Atoms form compounds because atoms in a compound tend to have the electron configuration of a noble gas this is the octet rule.

The correct match of the given statement are 1 - f. ionic compound, 2- d. formula unit, 3 - e. electron dot structure, 4- b. alloy, 5- k. metallic bond, 6- a. halide ions, 7- j. valence electrons, 8- h. coordination number, 9 - c. octet rule, 10- i. chemical formula.

Ionic compounds are made up of oppositely charged ions that are kept together in a crystal lattice. The formula unit is the lowest whole-number ratio of ions in an ionic compound.  

The coordination number is the number of ions with opposite charges that surround each ion in a crystal. Halide ions are halogen atom ions that are negatively charged.

Elements are made up of atoms, and the electron(s) in the atom's highest occupied energy level are known as valence electrons. The metallic bond refers to the attraction of free-floating valence electrons to positively charged metals in metals.

The electron dot structure or Lewis structure is a representation of the valence electrons as dots around the symbol for an element for atoms.

A compound or an alloy is a mixture of components. A metal is frequently present in an alloy.

The chemical formula is used for compounds. The types and numbers of atoms in the smallest representative unit are displayed.

The octet rule states that atoms in a compound tend to have the electron configuration of a noble gas.

Therefore, the correct matches are: 1 - f. ionic compound, 2- d. formula unit, 3 - e. electron dot structure, 4- b. alloy, 5- k. metallic bond, 6- a. halide ions, 7- j. valence electrons, 8- h. coordination number, 9 - c. octet rule, 10- i. chemical formula.

Learn more about ionic compound, here:

https://brainly.com/question/30420333

#SPJ6

The given question is incomplete, so the most probable complete question is,

Match the correct statement with their appropriate terms:

Compound composed of cations and anions, the forces of attraction that bind oppositely charged ions together.Lowest whole-number ratio of ions in an ionic compound.A depiction of the valence electrons as dots around the symbol for an element.A mixture of two or more elements, at least one of which is a metal.The attraction of the free-floating valence electrons for the positively charged metal.Ions of the halogen atoms.The electron(s) in the highest occupied energy level of an atom.The number of ions of opposite charge that surround each ion in a crystal.Atoms in a compound tend to have the electron configuration of a noble gas.Shows the kinds and numbers of atoms in the smallest representative unit.

why is seawater a better conductor of electricity than freshwater?

Answers

Answer:

please refer to the attachment above;)

Answer:

Because it contains Na+ and Cl- ions, Which are conductors of electricity

Explanation:

please help :) hope you have a good day

Answers

Answer:

the volume of the gas will decrease

K2HPO4 is a highly water-soluble salt. It can be used as a buffering agent, food additive, or
fertilizer. The neutralization of phosphoric acid with potassium hydroxide can be used to form
potassium hydrogen phosphate.
H3PO4 + 2KOH K2HPO4 + 2H2O
100 g of phosphoric acid (H3PO4) is reacted with excess potassium hydroxide. The final mass
of K2HPO4 produced is found to be 163 g.
What is the percent yield?

Answers

Answer:

91.7%

Explanation:

The percent yield when it could be used as a buffering agent should be considered as the 91.74%.

Calculation of the percent yield:

Since we know that

Number of moles = Mass in gram / Molar mass

And,

Molar mass of H3PO4 = 97.994 g/mol

So,

Number of moles of H3PO4

= 100 g / 97.994 g/mol

= 1.02 mol

Now

Molar mass of K2HPO4 = 174.2 g/mol

So,

Theoretical yield of K2HPO4 = 174.2 g/mol * 1.02 mol

= 177.684 g

So finally

Percent yield = Actual yield * 100 / Theoretical yield

= 163 g * 100 / 177.684 g

= 91.74%

hence, The percent yield when it could be used as a buffering agent should be considered as the 91.74%.

learn more about percentage here: https://brainly.com/question/14849541

Hello, this is a science task and it is due today I would really appreciate it if you guys can help me answer and explain what is the difference between expansion and contraction:) I will mark brainliest!

Answers

Answer:

Expansion: increase in size Contraction: decrease in size

Explanation:

The increase in size of an object on heating is called expansion where as the decrease in size of an object on cooling is called contraction.

Which of these statements is false?
A. All matter is made up of atoms.
B. Atoms are made up of protons,
neutrons, and electrons.
C. Atoms contain chemical bonds.
D. Atoms are the smallest particles of
elements.

Answers

Answer:

C is the false one atoms contain chemical bonds

Answer:

C. Atoms contain chemical bonds.

Reason:

Atoms don't have any chemical bonds. Molecules are the particles have chemical bonds.

Which of the following has the strongest gravitational field?
A. the sun
B. the earth
C. a football player
D. a tree

Answers

Answer:

A

Explanation:

Answer:

the sun , option A hope it helps

Antonio and Addie want to know if perfume fumes affect plant height. They place five identical bean plants in five identical light boxes. In four of the boxes, they place 200 milliliters (mL) of perfume at different distances from the plants, and they make observations twice a week for one month. Which choice best identifies the observation data that should be included in their data table?

Answers

Answer:

I think its C I'm sorry if I'm wrong good luck guys!

Explanation:

10. Imagine that the unknown solution contains aqueous ammonium sulfate, which is commonly used in fertilizer. For the precipitation of barium sulfate after mixing aqueous ammonium sulfate solution and barium chloride solution (the reactants), write the (1) balanced molecular equation, (2) the complete ionic equation, (3) the net ionic equation AND identify the spectator ions, if any.

Answers

Answer:

(1) (NH₄)₂SO₄(aq) + BaCl₂(aq) ⇒ BaSO₄(s) + 2 NH₄Cl(aq)

(2) 2 NH₄⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2 Cl⁻(aq) ⇒ BaSO₄(s) + 2 NH₄⁺(aq) + 2 Cl⁻(aq)

(3) SO₄²⁻(aq) + Ba²⁺(aq) ⇒ BaSO₄(s)

(4) NH₄⁺ and Cl⁻

Explanation:

(1) Let's consider the molecular equation that occurs after mixing aqueous ammonium sulfate solution and barium chloride solution. This is a double displacement reaction.

(NH₄)₂SO₄(aq) + BaCl₂(aq) ⇒ BaSO₄(s) + 2 NH₄Cl(aq)

(2) The complete ionic equation includes all the ions and insoluble species.

2 NH₄⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2 Cl⁻(aq) ⇒ BaSO₄(s) + 2 NH₄⁺(aq) + 2 Cl⁻(aq)

(3) The net ionic equation includes only the ions that participate in the reaction (not spectator ions) and the insoluble species.

SO₄²⁻(aq) + Ba²⁺(aq) ⇒ BaSO₄(s)

(4) The spectator ions are NH₄⁺ and Cl⁻.

According to this video, how do scientists use data to study/monitor earthquakes and tsunamis?​

Answers

Answer:

ewan ko po

Explanation:

sana makatulong

3.Which of these is NOT part of the cell theory? * "

all living things are made of cells
Ocells come only from other cells
cells are the smallest living unit of an organism
O all living things have blood cells

Answers

Answer:

Cells are the smallest living unit of an organism

Answer:

all living things living things have blood cells

Explanation:

this is because robert hooke did not make this apart of the theory

What is an electrolytic cell?

Answers

Answer:

An electrolytic cell is a cell that converts electrical energy into chemical energy.

Any device in which electrical energy is converted to chemical energy or vice versa is referred to as an electrolytic cell. A typical cell consists of two metallic or electronic conductors held apart and in contact with an electrolyte, which is usually a dissolved or fused ionic compound.

What is an electrolytic cell ?

An electrolytic cell is a type of electrochemical cell that uses an external source of electrical energy to force a chemical reaction that would not occur otherwise. A voltage applied between the cell's two electrodes, an anode and a cathode immersed in an electrolyte solution, serves as the external energy source.

Electrons in the form of an electric current are deliberately pumped through the chemicals in the section to induce an oxidation-reduction reaction. An electrolytic cell is a setup used to electrolytically decompose water into hydrogen and oxygen.

Electrochemical cells that generate an electric current are known as voltaic or galvanic cells, whereas those that generate chemical reactions, such as electrolysis, are known as electrolytic cells.

Thus, Any device in which electrical energy is converted to chemical energy or vice versa is referred to as an electrolytic cell.

To learn more about electrolytic cell, follow the link;

https://brainly.com/question/4030224

#SPJ5

Hail is falling down from the sky at 50 miles per hour. Is this an example of speed,
velocity or acceleration?

Answers

Explanation:

tgggghhhhijyyhhjjjjjjjj

Choose the combination of factors that creates fog. Record the description of the factors in the Student Guide,

Relative Humidity


Air Temperature


Air Pressure


Check

Pause

Answers

Answer:

Relative Humidity

Air Temperature

Explanation:

Relative humidity  and air temperature are the factors that creates fog. When the moist and warm air makes contact with the cooler air, water vapor condenses due to low temperature of that region that causes for the formation of fog. So we can say that relative humidity  and air temperature are the main factors for the formation of fog in that region.

Answer:

High Cold High

Explanation:

1. Mixing Water at Two Temperatures
a. One flask contains 150.0 g water at 20.0 °C. A second flask contains 350.0 g water at 95.0 °C. If the two water samples are mixed, what will the final temperature of the water be?
-Assume that the density of water it 1.000 g/cm^3
-The specific heat capacity for water is 4.184 J/g °C​

Answers

Answer:

[tex]T_f=72.5\°C[/tex]

Explanation:

Hello!

In this case, since this a problem in which the cold water is heated by the hot water, we can write:

[tex]Q_{hot}+Q_{cold}=0[/tex]

Thus, by plugging in the mass, specific heat and temperatures, we obtain:

[tex]m_{hot}C_{hot}(T_f-T_{hot})+m_{cold}C_{cold}(T_f-T_{cold})=0[/tex]

Now, we can also write:

[tex]m_{hot}(T_f-T_{hot})+m_{cold}(T_f-T_{cold})=0[/tex]

Then, after applying some algebra, it is possible to obtain:

[tex]T_f=\frac{m_{hot}T_{hot}+m_{cold}T_{cold}}{m_{hot}+m_{cold}}[/tex]

If we plug in, we obtain:

[tex]T_f=\frac{350.0g*95.0\°C+150.0g*20.0\°C}{350.0g+150.0g}[/tex]

[tex]T_f=72.5\°C[/tex]

Best regards!

After adding 20.0 mL of 5% NaOH solution into the remaining organic layer, followed by mixing and venting, the solution separated into two distinct layers. Match the following: Group of answer choices The top layer was the ______________ layer. [ Choose ] 9-fluorenone was most soluble in the ____________ layer. [ Choose ] deprotonated chloroanilic acid was most soluble in the _____________ layer. [ Choose ] The bottom layer was the __________________ layer. [ Choose ] The organic layer was a ________________ colored solution. [ Choose ] The aqueous layer turned into a _____________ colored solution. [ Choose ]

Answers

Answer:

The top layer was the organic layer.

9-fluorenone was most soluble in the organic layer.

Deprotonated chloroanilic acid was most soluble in the aqueous layer.

The bottom layer was the aqueous layer.

The organic layer was a yellow colored solution.

The aqueous layer turned into a pink colored solution.

what is the chemical equation for methamphetamine ​

Answers

Answer:

C10H15N is the chemical equation for methamphetamine

The chemical formula for methamphetamine or meth is C10H15N

Please help :) hope you have a good day

Answers

Have a wonderful day :) thanks for the points

b. If you have 50 grams of Molybdenum-99, how many grams will remain
after 11 days?

Answers

Answer:

6.25gm

half life is 66hrs 11 days is 24*11 then take that and divide by 66 to find out how many time it will have halved and half 50 by that many times

Explanation:

If you have 50 grams of Molybdenum-99, after 11 days, 2.7 g will remain.

Molybdenum-99 follows first-order decay.

What is first-order decay?

First-order decay means that for a population of atoms (e.g. radioactive), molecules, or anything else, a constant fraction/unit time is converted to something else.

The half-life (th) of Mo-99 is 66 h.

We will find its rate constant (k) using the following expression.

k = ln2 / th = ln2 / 66 h = 0.011 h⁻¹

Next, we will convert 11 days to hours, knowing that 1 day = 24 h.

11 d × 24 h/1 d = 264 h

If we start with 50 g of Mo-99, we can calculate the remaining mass after 264 h using the following expression.

[tex][Mo] = [Mo]_0 \times e ^{-k \times t} }\\\\[Mo] = 50g \times e ^{-0.011 h^{-1} \times 264 h} } = 2.7 g[/tex]

where,

[Mo] is the final amount of Mo-99.[Mo]₀ is the initial amount of Mo-99.t is the elapsed time.

If you have 50 grams of Molybdenum-99, after 11 days, 2.7 g will remain.

Learn more about first-order decay here: https://brainly.com/question/14478152

What is delta Gº for the following reaction at 25 °C?
CO(g) + 2 H2(g) = CH OH(9)
Ky = 2.1 x 10-4

Answers

Answer:

21 kJ/mol

Explanation:

Step 1: Given and required data

Temperature (T): 25 °C (298 K)Equilibrium constant (Kc): 2.1 × 10⁻⁴Ideal gas constant (R): 8.314 J/K.mol

Step 2: Write the balanced equation at equilibrium

CO(g) + 2 H₂(g) ⇄ CH₃OH(g)

Step 3: Calculate the standard Gibbs free energy of the reaction (ΔG°)

We will use the following expression.

ΔG° = - R × T × ln Kc

ΔG° = - (8.314 J/K.mol) × 298 K × ln 2.1 × 10⁻⁴ = 2.1 × 10⁴ J/mol = 21 kJ/mol

Other Questions
The table below shows data from a survey about the amount of time high school student spent reading in amount of time spent watching videos each week (without reading). Which response best describes outliers in the data sets?A. neither data set has suspected outliersB. The range of data is too small to identify outliersC. video has a suspected outlier in the 26-hour valueD. due to the narrow range of reading compared to video the video values of 18, 21, and 26 are all possible outliers Blood vessels that have valves in them: one of the major benefits of specialization is that help afap!!!!!!!!! i need facts about the Great Chicago Fire of 1871!!!!!! 12. 4x2 - 4y2 + 1622 - 16xz Timmy and Tommy are each earning money to go on a trip for school. In one weekend, Timmy earns a certain amount and tommy earns twice what Timmy earned plus $24. Altogether, they earned $174. what is 99.99/72? Plz help ASAP! Describe how population studies can be conducted in a school garden Which genre would be most appropriate for a piece of writing encouraging students to dress up for homecoming week?a short storya lyrical poema persuasive essaya compare / contrast es The frequency table shows the results of tossing a number cube 50 times. Which statementis reasonable, based on the data?The number 2 will be the next number tossed.Top Number on CubeFrequency18Tossing an even number is more likely thantossing an odd number.21036410The probability of tossing the number 2 is to5769The number 4 is half as likely to be tossed asthe number 3 Look at the equation below. HELP ASAP PLEASE THIS IS VERY IMPORTANT EXPLAIN FOR BRAINLIST AND GET IT RIGHT FOR BRAINLIST TY! Which of the following African-Americans most influenced American music? The variables x and y are proportional. Use the values to find the constant of proportionality. Then write an equation that relates x and y.When y=72 and x=3.K = ?y = ? 1. Consider the figure below.Determine the measure of each interior angle of A MAN and classify thetriangle. Match the term to its definition (Hint: Look at the bottom of the article)Column A1.Winter Storm Watch:Winter Storm Watch2.Winter Storm Warning:Winter Storm Warning3.Frost/Freeze Warning:Frost/Freeze Warning4.Ice Storm Warning:Ice Storm Warning5.Blizzard Warning:Blizzard Warning6.Winter Weather Advisory:Winter Weather Advisory7.Heavy Snow Warning:Heavy Snow WarningColumn Ba.Conditions from recent winter weather can be hazardous (especially for drivers).b.A combination of snow and wind will create limited visibility, drifting snow, and dangerous wind chillsc.There will be more than four inches in 12 hours or six inches in 24 hours.d.A winter storm is likely. The storm may include sleet, snow, ice, or a combination of them.e.There will be dangerous accumulations of icef.The winter storm is expected to enter the areag.The temperature will dip below freezing [tex]\frac{28}{54} = \frac{2x+8}{5x-4}[/tex] Help please! Asap!! Will give brianliest! pls help I stuck this is so hard Question 9Earthquakes are caused by shaking in the Earth's crust due to the rapid release of ______ energy.a) mechanical b) electromagnetic c) chemical