New York City is one of the densest cities in the world, with millions of people squeezed into a mere
303 square miles. Although it has the world's largest subway system, traffic can still be quite bad,
particularly at rush hour. The city decided that it would be a good idea to encourage more people to
use bicycles. If more people rode bicycles, the roads would be less clogged with cars. Also, when you
ride a bicycle, you are exercising, which makes you healthy. But how can you encourage people to ride
more bikes?
The city came up with an innovative solution. In 2013, city workers began installing long racks of
bicycles in different neighborhoods. These bicycles were, for a small fee, available for anyone to use. A
person could ride the bicycle from one bike rack to another bike rack and park it there. This system
was ideal for people who did not own bikes or who wanted to take a bicycle on a short ride without
having to return it to the place they took it from. This also made it possible to move quickly between
areas that did not connect easily by the subway. The city hoped that people would start using these
bicycles instead of taxis or other kinds of cars.
While the city installed the bikes in part because of concerns about traffic, it was also interested in
another question: how we use and spend energy. Any time an object is in motion, it is both producing
energy and, in many cases, expending energy. For example, a car does not just move because we
want it to move. It is powered by a special kind of engine, called an internal combustion engine that
burns fuel. When this fuel is burned, it causes a cylinder to spin in circles. This cylinder is connected to
the wheels of the car. As the cylinder spins, so do the wheels. So, one type of energy - fuel - is
transformed into another type of energy - forward motion. Energy contained in the motion of an object
is called "motion energy."
Just as cars can be considered a kind of energy conversion device, converting fuel to forward motion, so can bicycles. When you step on the pedals of a bicycle, it causes the wheels of the bicycle to spin,
pushing the bicycle forward. The energy of your foot pressing down is converted into energy that
propels the bicycle. Nearly all transportation - airplanes, trains, pogo sticks - can be thought of as
devices that take one form of energy and make it into another form of energy.
When there is a change in one of the forms of energy used to power modes of transportation, then the
energy generated by these devices changes as well. Let's say you're pedaling very fast on a bicycle.
You are exerting a lot of energy as you do this. You can tell because your heart rate may increase, you
may breathe harder, and you may begin to sweat - a sign that your body is trying to cool itself. This is
producing a lot of motion energy in the bicycle because you are causing it to move very fast. But if you
stop pedaling, then the bicycle will begin to slow down, and the motion energy in the bicycle will
decrease. You will also be expending less energy. Your heart rate and your breathing will slow down,
too. The decline in your own motion energy - the movement of your feet - is causing the motion
energy of another object - the bicycle - to fall at about the same rate.
In the early days of the program, the bike racks were only moderately popular. People were still getting
used to the idea of borrowing a bike for a short time at one location, riding it, and then leaving it in
another location. Perhaps another reason that people were initially reluctant to use the bike racks is
that they were introduced during a very hot week, at the beginning of summer. As discussed above,
when you ride a bicycle, you often sweat. This is particularly true when the temperature is high,
because your body produces sweat as a way of trying to keep your body cool. If your body gets too
hot, you can get sick, so it's in your body's interest to maintain a constant temperature.
How much the temperature of a body increases when it gets warm depends on a number of different
factors. While it makes sense that one person in 100-degree heat will get hotter than a person in 75-
degree heat, even if two people are exposed to the same temperature, their bodies may react
differently. In fact, one person may get much hotter than the other. This is because the amount of heat
- which is a form of energy - needed to change the temperature of another object depends on the
properties of that object. For example, a person who is wearing a sweatshirt in summer is likely to get
much hotter than a person who is wearing a t-shirt. This is because the sweatshirt insulates the
person, trapping heat inside. The t-shirt, which is more open, lets the heat escape. So, even if the
amount of heat energy directed at the person is the same, the temperatures of different people will
react differently.
That raises another question: why does sweat makes people colder? This has to do with a special
property of heat. Heat is a kind of energy, and energy moves spontaneously from hotter regions or
objects to colder ones. So, consider what happens when your body releases sweat. When it is
released, sweat is colder than your body's temperature. When it is on the surface of your skin, it draws
the heat from your skin into the water, because heat migrates from warm areas to cold ones. This
causes the sweat to warm up. Then the sweat rises into the air and takes some of your body heat with
it, cooling the body down.
Your body is constantly monitoring its own temperature. Many of the buildings in New York have air
conditioning in the summer. When you walk from the hot street outside to the cool lobby of a tall office
building, you can feel the change immediately. After a while, your body temperature will go down. This
is because, just as the heat from your body moves to the sweat on your skin, it will also move to the
cool air produced by the air conditioning. When your body gets cool enough, it will no longer need to
produce sweat to cool you down.
As people continue to ride bicycles, you can expect their collective body temperatures to rise, as their
bodies produce energy to power the bicycles and they spend more time outdoors in the hot sun. If the
city chooses to install more bikes, then it may also want to install more air conditioning - or pass out
more sticks of deodorant
Question 1: When you exert energy, your heart rate may increase.
Question 2: It may be a reason why bike racks were only moderately popular at first.
Question 3: “This is because, just as the heat from your body moves to the sweat on your skin, it will also move to the cool air produced by the air conditioning.”
to help people stay cool and fresh while they bike around the city. By taking steps to keep people comfortable while they ride bicycles, the city can encourage more people to use this sustainable and healthy mode of transportation. In this way, the city can reduce traffic congestion, promote physical activity, and contribute to a cleaner and healthier environment for all residents.
Based on the passage, what can the reader conclude about the relationship between exerting energy and heart rate?(1 point)
Responses
When you exert energy, your heart rate always decreases.
When you exert energy, your heart rate always decreases.
When you exert energy, your heart rate always stays the same.
When you exert energy, your heart rate always stays the same.
When you exert energy, your heart rate may increase.
When you exert energy, your heart rate may increase.
When you exert energy, your heart rate always increases.
When you exert energy, your heart rate always increases.
Question 2
What can the reader conclude about the relationship between high temperatures and sweating?(1 point)
Responses
It may be a reason why bike racks were only moderately popular at first.
It may be a reason why bike racks were only moderately popular at first.
It may be a reason why sweatshirts are popular in the summer.
It may be a reason why sweatshirts are popular in the summer.
It may be a reason why traffic is bad in New York City.
It may be a reason why traffic is bad in New York City.
It may be a reason why bike racks were in high demand when they were first introduced.
It may be a reason why bike racks were in high demand when they were first introduced.
Question 3
When you move from a hot temperature to a colder temperature, your body will eventually stop sweating. Which evidence from the passage best supports this statement?(1 point)
Responses
“If your body gets too hot, you can get sick, so it's in your body's interest to maintain a constant temperature.”
“If your body gets too hot, you can get sick, so it's in your body's interest to maintain a constant temperature.”
“This is because, just as the heat from your body moves to the sweat on your skin, it will also move to the cool air produced by the air conditioning.”
“This is because, just as the heat from your body moves to the sweat on your skin, it will also move to the cool air produced by the air conditioning.”
“This is particularly true when the temperature is high, because your body produces sweat as a way of trying to keep your body cool.”
“This is particularly true when the temperature is high, because your body produces sweat as a way of trying to keep your body cool.”
“So, one type of energy - fuel - is transformed into another type of energy - forward motion.”