compare and contrast a transverse wave and a compressional wave Give an example for each type

Answers

Answer 1

Answer:

Transverse waves oscillate perpendicular to the direction of the wave (e.g. any electromagnetic wave like radiowaves, x-rays...) whilst compressional waves oscillate in the same direction of the wave (e.g. sound waves)

Explanation:


Related Questions

URGENTLY NEED HELP

This is a 2 part question

42) You pull downward with a force of 28 N on a rope that passes over a disk-shaped pulley of mass 1.2 kg and radius 0.075 m. The other end of the rope is attached to a 0.67-kg mass. (a) Is the tension in the rope the same on both sides of the pulley? If not, which side has the greater tension? (b) Find the tension in the rope on both sides of the pulley.

Answers

Answer:

The net force on the hanging mass is thus

2 T Mg     18 6.6 N 11.4 N

, enough to accelerate it upward at

17 m/s2

. The angular acceleration of the pulley is thus

   

2 2

Explanation:

The tension in the rope on both sides of the pulley 20.21N.

To solve this problem, we'll need to consider the forces acting on both sides of the pulley and apply Newton's second law of motion. Let's break it down step by step:

(a) Is the tension in the rope the same on both sides of the pulley?

No, the tension in the rope is not the same on both sides of the pulley. The side with the greater mass attached will experience a greater tension in the rope.

(b) Find the tension in the rope on both sides of the pulley:

Calculate the gravitational force on each mass:

Gravitational force on the pulley: Fpulley = mpulley * g, where mpulley is the mass of the pulley and g is the acceleration due to gravity (approximately 9.8 m/s²).

Gravitational force on the hanging mass: Fhanging = mhanging * g, where m_hanging is the mass of the hanging mass.

Calculate the net force on the pulley:

Net force on the pulley is the difference between the tension forces on either side: Fnet = TLeft - Tright.

Apply Newton's second law to the pulley:

For the pulley, Fnet = mpulley * a, where a is the acceleration of the pulley. Since the pulley is assumed to be massless, we can use the relationship a = α * r, where α is the angular acceleration and r is the radius of the pulley.

Use the relationship between linear acceleration and angular acceleration:

α = a / r.

Equate the torque due to the tension to the moment of inertia times the angular acceleration:

τ = I * α, where τ is the torque, I is the moment of inertia of the pulley, and α is the angular acceleration.

Substitute the expression for α and solve for the net tension:

Tnet = (τ / r) = (I * α) / r = (1/2 * mpulley * r² * α) / r = (1/2 * mpulley * r * a).

Now, substitute the expression for a from step 3 and solve for the net tension:

Tnet = (1/2 * mpulley * r * α) = (1/2 * mpulley * r * (a / r)) = (1/2 * mpulley * a).

Substitute the expression for a from step 2 (Fnet = mpulley * a) and solve for the net tension:

Tnet = (1/2 * Fnet).

Now, you can find the tensions on each side of the pulley:

Tleft = Tnet + Fhanging

Tright = Tnet - Fpulle

To know more about tension

https://brainly.com/question/16943376

#SPJ2

The force as a function of displacement of a moving object is presented by the graph. How much work is done when the object moves from 5 m to 8 m? *

Answers

Answer:

Explanation:

Work is the area under the curve between the limits

W = ½(5)(8 - 5) = 7.5 J

The work done when an object moves from 5 m to 8 m is 7.5 J.

Work done

The work done in moving an object from one point to another is equal to the product of force and displacement of the object.

W = Fs

Area under a curve

The work done on an object is equal to area under the curve

The area between point 5 m and 8 m = ¹/₂ x (8 - 5) x 5 = 7.5 J

Thus, the work done when an object moves from 5 m to 8 m is 7.5 J.

Learn more about work done here: https://brainly.com/question/8119756

Select the correct answer. Chloe is playing the flute some distance away from a crowd. If the atmospheric temperature is 15°C, what is the speed of the sound traveling from the flute? A. 340 meters/second B. 330 meters/second C. 320 meters/second D. 310 meters/second E. 300 meters/second

Answers

Answer:

A. 340 meters/second

I think this is the right answer.

The degree of coldness or hotness is different for different objects. Explain with an example

Answers

Answer:

Explanation:

The degree of hotness and coldness of air is known as temperature and is measured with a thermometer in degrees-Fahrenheit or degrees-Celsius. Mercury is the only one in the liquid state at room temperature. It is used in thermometers because it has a high coefficient of expansion. The flow of heat will be always from higher to lower temperature.

PLS MARK ME WITH BRAINLEST

a rectangular block has the density of 350g/cm3 the dimensions are 3.5 6.cm 2.5
cm calculate the mass of the bock​

Answers

Answer:

18375g

Explanation:

[tex]\boxed{density = \frac{mass}{volume} }[/tex]

[tex]∴ mass = density \times volume[/tex]

Let's find the volume of the rectangular block.

Volume

= length ×breadth ×height

= 3.5 ×6 ×2.5

= 52.5cm³

Mass of the block

= 350(52.5)

= 18375g

The ability to do work and cause change is called

Answers

Answer:

I am pretty sure it is called energy.

The answer is energy, when you work on an object some of your energy is transferred to that object with that being said work is the transfer of energy.

The diagram below shows a child pulling a 50.-kg friend on a 20 kg sled by applying a 300. newton force on the sled rope at an angle of 40 degrees with the horizontal. The sled moves at constant velocity as the person pulls with the 300 N force.

Answers

The vertical component of the applied force on the sled is 192.84 N.

The given parameters:

Mass of the friend, M = 50 kgMass of the sled, m = 20 kgApplied force, F = 300 NInclination of the force, θ = 40 ⁰

The vertical component of the 300 N force is calculated as follows;

[tex]F_y= F \times sin(\theta)\\\\F_y = 300 \times sin(40)\\\\F_y = 192.84 \ N[/tex]

Thus, the vertical component of the applied force on the sled is 192.84 N.

Your question is not complete, the missing part of the question is below:

The vertical component of the 300 N force is approximately?

Learn more about vertical component of forces here: https://brainly.com/question/7181504

In three to five sentences, identify the acid, base, conjugate acid, and conjugate base. Use patterns in the periodic table to explain why the substances you identified acted as the acid and the base in this reaction.

Answers

A conjugate acid is formed from the base  by accepting a proton from the acid .

A conjugate base is obtained from the Brownstead - Lowry acid when it looses a proton while the conjugate acid is obtained from the Brownstead - Lowry base when it accepts a proton. In the Brownstead - Lowry sense, acid base reaction involves the loss or gain of a proton.

Consider the hypothetical reaction; AH + :B ⇄ BH + :A. The specie BH is the conjugate acid while the specie  :B is the  Brownstead - Lowry base . The specie :A is the conjugate base while the specie AH is the  Brownstead - Lowry acid.

Learn more about conjugate acid: https://brainly.com/question/10468518

A stone of mass m = 1.05 kg is released from a height of h = 2.1 m into a pool of water. At a time of t = 1.83 s after hitting the surface of the water, the stone's velocity has decreased by 50%.
What is the magnitude of the average force the stone experiences, in newtons, during the time t?

Answers

Answer:

Explanation:

ignoring air resistance, the kinetic energy at water impact will equal the potential energy converted

½mv² = mgh

v = √(2gh)

v = √(2(9.81)2.1) = 6.4188... m/s

after impact, an impulse will result in a change of momentum.

There is a downward impulse due to gravity equal to the weight of the stone and an upward average force due to water resistance and buoyancy force.

FΔt = mΔv

(F - mg)Δt = m(vf - vi)

(F - mg) = m(vf - vi)/Δt

F = m(vf - vi)/Δt + mg

F = m((vf - vi)/Δt + g)

F = 1.05(((½(-6.4188) - -6.4188)/ 1.83) + 9.81)

F = 12.14198...

F = 12.1 N

The magnitude of the average force the stone experiences, will be 12.1 N.

What is force?

Force is defined as the push or pulls applied to the body. Sometimes it is used to change the shape, size, and direction of the body. Force is defined as the product of mass and acceleration. Its unit is Newton.

The given data in the problem is;

m is the stone mass = 1.05 kg

The height is h, = 2.1 m i

The time is, t = 1.83 s

Velocity decreased by 50%.

From the law of conservation of energy the kinetic energy is equal to the potential energy;

[tex]\rm \frac{1}{2} mv^2 = mgh \\\\ v = \sqrt{2gh}\\\\ v = \sqrt{2 \times 9.81 \times 2.1 } \\\\ v= 64188 \ m/sec.[/tex]

From Newton's second law of motion, the impulsive force is equal to the change in momentum;

[tex]\rm F \triangle T = m \traingle v \\\\ (F - mg) = \frac{v_f-v_i}{\triangle t } \\\\ F = \frac{v_f-v_i}{\triangle t } + mg \\\\ F =m\frac{v_f-v_i}{\triangle t + g} \\\\ F= 12.14 98 \\\\ F=12.1 N[/tex]

Hence the magnitude of the average force the stone experiences, will be 12.1 N.

To learn more about the force refer to the link;

https://brainly.com/question/26115859

How is probability used in blood typing

Answers

Blood Type O AB

Probability 0.45 0.04

Which type of muscle cell can have multiple nuclei

Answers

Answer:

Skeletal Muscle cells

Skeletal muscle cells are long, cylindrical, and striated. They are multi-nucleated meaning that they have more than one nucleus. This is because they are formed from the fusion of embryonic myoblasts.

Answer:

skeletal muscle cells can have multiple nuclei

Explanation:

This is because they are formed from the fusion of embryonic myoblasts.

True or False. Abraham and Sarah were in agreement regarding God's command to sacrifice Isaac.

Answers

Answer:

Explanation:

Not in Genesis. The proposed sacrifice of Isaac was all Abraham's doing. Sarah was not present and could not, therefore offer any input. It might have been covered in other Jewish writings, but it is not recorded in Genesis.

Since the book most widely used by Everyone is the Bible, I would answer false.

Using the figure shown, if I₃= 1.17 A, then (I₁ , I₂) A is:

a- (3.17 , 2.00)
b- (1.33 , 0.17)
c- (1.67 , 0.50)
d- (1.27 , 0.10)

Answers

The value of the current in each arm of the circuit is given by Kirchhoff's

Rules.

The correct option for (I₁, I₂) is; b-. [tex]\underline{(1.33, \ 0.17)}[/tex]

Reasons:

By Kirchhoff's junction rule, we have that the sum of current at a junction is given as follows;

[tex]\displaystyle \mathbf{ \sum \limits_{k = 1}^ n I_K} = 0[/tex]

Which by the direction of the currents in the given circuit diagram, we have;

I₁ - (I₃ + I₂) = 0

Therefore;

I₁ = I₃ + I₂

According to Kirchhoff's loop rule theory, we have;

[tex]\displaystyle \mathbf{\sum \limits_{k = 1}^ n V_K} = 0[/tex]

In the loop having the 2 Volts emf., we have;

-I₃·R₁ + 2 + I₂·R₂ = 0

I₃ = 1.17 A

R₁ = 2 Ω

R₂ = 2 Ω

Which gives;

-1.17 × 2 + 2 + I₂×2 = 0

I₂ × 2 = 2.34 - 2 = 0.34

I₂ = 0.34 ÷ 2 = 0.17

I₂ = 0.17 A

From the loop having the 7 Volts emf. we have;

7 - 0.17×2 - I₁ × 4 - I₁ × 1 = 0

Which gives;

7 - 0.34 - 5·I₁ = 0

5·I₁ = 7 - 0.34 = 6.66

I₁ = 6.66 ÷ 5 = 1.332

Therefore;

[tex]\underline{\mathbf{(I_1, \, I_2)} = (1.33, \, 0.17)}[/tex]

Learn more about electric circuits here:

https://brainly.com/question/2608877

When a 1 is on the input of an inverter, what is the output?​

Answers

Answer:

When the input to an inverter is high (1) the output is low (0); and when the input is low, the output is high.

Suppose you want to make the demonstration more dramatic by attracting as much hair as possible with the balloon. Which of the following is the best choice to accomplish your goal? A. Decrease the electric force by holding the balloon closer to the hair. B. Increase the electric force by rubbing the balloon for a longer period of time. C. Decrease the electric force by using a larger balloon. D. Increase the electric force by holding the balloon farther away from the hair.

Answers

Answer:

B. Increase the electric force by rubbing the balloon for a longer period of time.

Explanation:

A wire that is 1.0 m long with a mass of 90 g is under a tension of 710 N. When a transverse wave travels on the wire, its wavelength is 0.10 m. What is the frequency of this wave? ​

Answers

Answer:

890 Hz

I hope you liked my answer. Thank You!

The gradual increase in activity over time is called

Answers

Answer:Progression is the way in which an individual should increase the load. It is a gradual increase either in frequency, intensity, or time or a combination of all three components.

Explanation:

the gradual increase in activity over time is called progression

Suppose a bulldozer is being hauled at 50 km/h to a construction site on the back of a flatbed truck. From which reference point would the bulldozer not appear to be moving?

Answers

Answer:

from someone watching the bulldozer from the cab of the truck or from elsewhere on the flatbed.

Explanation:

if the force acting on a body of mass 40 k.g is doubled by how much will the acceleration change​

Answers

Answer:

Explanation:

Ignoring friction, the acceleration will double

F = ma

2F = m(2a)

25.Figure 22.22 shows a plot
of potential versus position
along the x-axis. Make a plot
of the x-component of the
electric field for this situation.

Answers

The relationship between the potential and the electric field allows to find the results for the value of the electric field as a function of the distance is:

In the attachment we see the graph of the electric field as a function of distance.

Electric potential is defined by the change in potential energy of a test charge between two points, between the value of the test charge.

          dV = - E . ds

          E = [tex]- \frac{dV}{ds} \ \hat s[/tex]  

Where the bold letters indicate vectors, V is the potential difference, E the electric field and s the path.

Let's apply this expression for each section of the given graph:

1) section from x₀ = 0 to x_f = 2 m, the potential is V₀ = 2 V is constant.

  The derivative of a constant is zero.

        E = 0

2) Section between x₀ = 2 and x_f = 4 m, the potential varies linearly from V₀ = 2 v to V_f = -2 V.

We look for the equation of the line.

       V-V₀ = m (x- x₀)

We carry out the derivative.

      E = - m i ^

The slope (m) is:

       [tex]m= \frac{V_f - V_o}{x_f- x_o}[/tex]  

Let's calculate.

       [tex]m= \frac{-2 -2}{4-2} = \ -2 \ V/m[/tex]  

Let's substitute.

       E =  [tex]2 \hat i \ V/m[/tex]  

         

3) From x₀ = 4 to x_f = 4.5 m, the potential varies from V₀ = -2 to V_f = 0.

We look for the equation of the line and we derive.

      E = - m i ^

Let's  substitute.

      [tex]m = \frac{0-(-2)}{4.5-4} = \ 4 V/m[/tex]  

    E = - 4 [tex]\hat i[/tex] V / m

4) From x₀ = 4.5 m to x_f = 6m.  The potential is constant and the derivative of a constant is zero.

      E = 0

5) From x₀ = 6m to x_f = 8 m, the potential changes linearly from v₀ = 0 to V_f = 1 V

We look for the equation of the line and we derive.

       E = - m i ^

       [tex]m = \frac{1-0}{8-6} = \ 0.5 \ V/m[/tex]  

      E = - 0.5 [tex]\hat i[/tex] V/m

6) From x₀ = 8m to x_f = 9m, the potential changes linearly from V₀ = 1 V to V_f = -1.

We look for the equation of the line and we derive.

       E = - m i ^

       [tex]m = \frac{-1-1}{9-8} = \ -2 \ V/m[/tex]

Let's substitute.

       E = 2 [tex]\hat i[/tex] V/m

7) From x₀ = 9m to x_f = 10 m, the potential changes linearly from V₀ = -1 V to V_f = -2 V

     

We look for the equation of the line and we derive.

       E = - m i ^

       [tex]m = \frac{-2+1}{10-9} = \ -1 \ V/m[/tex]

Let's substitute.

       E = 1 [tex]\hat i[/tex]  V/m

In the attachment we can see these Electric fields as a function of distance.

In conclusion, the relationship between the potential and the electric field we can find the results for the value of the electric field as a function of the distance is:

In the attachment we see the graph of the electric field as a function of distance.

Learn more about the electric field here:  brainly.com/question/14306881

2. Define Lightning conductor. How does it work?

Answers

In Building, there are a host of protective devices that are installed to protect lives and properties, one of them is the Lightning Conductor that  a metal rod mounted on a structure and intended to protect the structure from a lightning strike. It works on the principle of induction

Principle of Operation of Lightning Conductor

The lightning conductor works on the principle of induction:

When a charged cloud passes by the building hosting the Lightning conductor, it gets a charge opposite to that of the cloud through the process of induction. They are Typically made from copper material.

Most Lightening conductors are made from copper materials.

Learn about Lightning Conductor:

https://brainly.com/question/2824044

The motor in a hairdryer is attached to a 3V battery. A current of 0.8A flows through the motor for 3 minutes. Calculate the total charge in this time.

Answers

The total charge in this time is equal to 144 Coulomb.

Given the following data:

Voltage = 3 VoltsCurrent = 0.8 AmperesTime = 3 minutes.

To calculate the total charge in this time:

First of all, we would convert the value of time in minutes to seconds.

Conversion:

1 minute = 60 seconds

3 minutes = 180 seconds

Formula for quantity of charge.

Mathematically, the quantity of charge is given by this formula:

[tex]Q=It[/tex]

Where:

Q is the quantity of charge.I is the current.t is the time measured in seconds.

Substituting the given parameters into the formula, we have;

[tex]Q = 0.8 \times 180[/tex]

Quantity of charge, Q = 144 Coulomb.

Read more on charges here: https://brainly.com/question/4313738

Answer:

960 watts

Explanation:

An airplane accelerates from rest down a runway at 9.50 m/s2 for 29.3 seconds when it
takes off. What is the distance traveled while taking off?

Answers

Answer:

Explanation:

s = ½at²

s = ½(9.50)(29.3²) = 4,077.8275

s = 4080 m

when rounded to the three significant digits of the question numerals.

please answer it I will mark it brainliest​

Answers

Explanation:

1) If you spot something you think might be hazardous in your workplace, report it to your employer and safety rep straight away. Your employer should then decide what harm the hazard could cause and take action to eliminate, prevent or reduce that harm. Read more about risk assessments .

2) Complex hazards are understood as various combinations of sources of hazards that lead to the accident occurrences. ... The term "natural-technological" applies to both human-induced intensification of natural risks and any accidents in the technosphere triggered by natural processes or phenomena.

3)Risk Evaluation : To determine who may be harmed. Risk Control : Taking preventive measures to control the impact of risk.

In general, to do an assessment, you should:

Identify hazards.

Determine the likelihood of harm, such as an injury or illness occurring, and its severity. ...

Identify actions necessary to eliminate the hazard, or control the risk using the hierarchy of risk control methods.

A hazard is something that can cause harm, e.g. electricity, chemicals, working up a ladder, noise, a keyboard, a bully at work, stress, etc. A risk is the chance, high or low, that any hazard will actually cause somebody harm.



Risk Identification : It is a process of characterizing hazards. Risk Analysis : A process of determining the impact of risk. Risk Evaluation : To determine who may be harmed.

PLEASE ASP HELP THIS WILL GIVE 50 POINT AND BRAINLIEST!!!!!!
In introductory physics, a typical cavendish balance for measuring the gravitational constant G use metal masses 2.39kg and 16g whose center are separated by 6.81cm calculate the gravitation force between these forces, treating each as a point mass located at the center of the sphere.

gravitational constant =6.67259 × 10⁻¹¹N·m²/kg²

Answers

Answer:

Explanation:

F = GMm/d²

F = 6.67259 x 10⁻¹¹(2.39)(0.016) / 0.0681²

F = 5.5019685...x 10⁻¹⁰ N

round as appropriate, probably no more than 3 significant figures.

Value of G seems low, but well within the 3 significant figures of the other numerals. I typically see G = 6.674 x 10⁻¹¹


Which is the answer

Answers

Answer:

no idea thanks you veryuch

8th grade science !
can someone help me with trying to understand this question for my homework especially how to understand the graph and use that for my evidence and help me give an idea of how should I write the evidence and reasoning?​

Answers

Answer:

for reasoning you could put -> the line is at the top at the left handed sided of the chart (also the beginning) slopes down towards the very bottom right handed side of the chart, symbolising less force as distance goes.

identify the origins of breakdown when using a spectrum analyzer

Answers

Four regions of the electromagnetic spectrum that astronomers use when observing objects in the space are the following enumerated answers.

1. First is Ultraviolet

2. Next is Infrared

3. Then the radio

4. Lastly the Visible lights.

These are the answers to the problem.

In a collision, a 30 kg ball moving at 3 m/s transfers all of its momentum to a 5kg ball. what is the velocity of the 3kg ball after the collision?

Answers

Answer:

Explanation:

Is it a 30 kg ball or a 3 kg ball?

Does not matter as we don't have to do actual calculations

If all of the momentum is transferred out of a mass, the velocity remaining must be ZERO

Who actually asked Abraham to sacrifice his son?

Answers

Answer:

Allah asked Abraham(Ibrahim)

Other Questions
Welcome to my attic. I'm positivethat there are a lot of metals inhere. had to remove itself fromWorld War I, because of the revolutionin its own country.A. The United StatesB. EnglandC. Russia Jack went to the ABC Casino to gamble. ABC offers its customers one free spin of the Million Dollar Wheel if they fill out an application form. Jack filled out the form, spun the Million Dollar Wheel, and won. However, now ABC refuses to pay, claiming that because Jack did not purchase his chance at the Million Dollar Wheel, Jack gave no consideration and therefore, no contract was formed. Identify the accurate statement. A. No contract was formed because Jack paid no money for his chance at the Million Dollar Wheel.B. No contract was formed because ABC did not sign any written contract as an obligation to do so.C. A contract was formed because filling out an application can constitute legal consideration.D. A contract was formed because no consideration is needed when a customer takes advantage of a "free" offer. Write [tex] \frac{10}{12} [/tex]in simplest form Neither of the girls completed their work.(Affirmative) Write a system of equations to describe the situation below, solve using any method, and fill in the blanks.Nicole and Josie are both selling cookie dough for a fundraiser. Although Nicole has already sold 4 tubs, Josie hasn't sold any yet. If Nicole starts selling 5 tubs per day and Josie begins selling 6 tubs per day, they will eventually sell the same amount of cookie dough. How many tubs will each sell? How many days will that take?Nicole and Josie will each sell tubs of cookie dough in days. finding the distance along a diagonal with the distance formula requires you evaluate a square root. true or false ? PLS HELP ASAP ILL GIVE BRAINLKEST PLS THANKS - Qu acciones debe adelantar el gobierno local ynacional para garantizar una buena calidad de vidapara todos los ancianos? how many health related fitness components are there slope y-intercept form of an equation for a line that has an x-intercept of "-3" and goes through (-2,2) What are our duties towards the nation? List them. Carson bought 50 pounds of rice for his restaurant. He cooked the rice and wanted to evenly divide it into 9 containers to be served later. How many pounds of rice should Carson put in each container? help plss Help help math Ill give points thanks _____ an important thing that must be done before other things.A achieveB scheduleC priority tickets at a particular movie theater have different rates for adults and children. On tuesday the theater sold 8 adult tickets and 9 tickets for 174. the next day the theater sold 5 adult tickets and 7 children tickets for 117. What is the price for the adult ticket and the price for the child ticket Write a sentence with each word of the vocabulary Read the text The Milky Way:The band that looks like milk in the night sky isn't actually milk, of courseit's a galaxy. A galaxy is a huge cluster of stars, dust, gas, and other objects bound together in space. Our Solar System, which includes the sun, Earth, and other planets, is part of the Milky Way galaxy. The Milky Way is about 14 billion years old. Almost 10 billion years older than our Solar System!It took many years to discover the Milky Way. In the early 1500s, Nicolaus Copernicus was the first to show that Earth was an object orbiting the Sun. In the early 1600s, Galileo Galilei used a basic telescope to show that the Milky Way was made up of countless stars. Then, in the late 1700s, William Herschel tried to map out the shape of the Milky Way. He did not realize that large portions of the galaxy were hidden by gas and dust, so he could not identify the true shape. Edwin Hubble had access to many powerful telescopes and tools to observe more objects in space. His work provided evidence that the Milky Way was only one of many galaxies in the universe. He also identified the spiral shape of our galaxy.Why was Herschel unable to correctly map out the shape of the Milky Way? He couldn't calculate the actual age of the Milky Way galaxy. He couldn't see through the Milky Way's gas and dust particles. He didn't know that the Earth and sun are part of the galaxy. He didn't know that the Milky Way was made up of many stars.marking as brainlest Check the box under each molecule in the table below that is an isomer of this molecule: What is the range of y = sin x?A. In72 ToB. -1Sys1c. -1SIS 1oD. All real numbers