Mass and weight
This Topic is About...
- I will learn the difference between mass and weight.
- I will see how gravity affects weight but not mass.
- I will measure mass and weight of different objects.
- I will decide when to repeat measurements to get better results.
- I will describe patterns in results and know when they don’t fit.
- I will draw a conclusion from my results.
- I will record my measurements in a table.
Let’s start learning about mass, weight, and gravity!
Key Words
- astronaut
- forcemeter
- mass
- newton
- rehabilitation
- weight
- weightlessness
Tap to Learn the Meanings!
- astronaut: A person who travels into space.
- forcemeter: A tool used to measure force or weight.
- mass: The amount of matter in an object, measured in kilograms.
- newton: A unit used to measure force or weight.
- rehabilitation: The process of recovering from an injury or illness.
- weight: The force of gravity acting on an object, measured in newtons.
- weightlessness: A condition where there is no gravity or very little, causing objects to float.
Great job learning new science words!
Mass and Weight
Mass is the amount of matter in an object. We measure mass in kilograms (kg). In everyday English we use the words weigh and weight to mean an amount in kilograms. However, this is technically incorrect because weight is the force caused by gravity, not the mass itself.
Effect of Gravity on Weight
Remember, all objects on Earth are pulled or attracted towards the center of the Earth by gravity. Weight is the amount of attraction on an object caused by gravity. Our weight changes when gravity changes, but our mass stays the same.
Weight on Other Planets
Objects have the same mass wherever they are. For example, you would have the same mass on the Moon or planet Jupiter. However, your weight would be different because it depends on gravity. The amount of gravity changes from planet to planet, so your weight would change depending on the strength of gravity. If you were on the Moon, you would weigh less than on Earth, even though your mass is the same.
Measuring Mass and Weight
We measure mass in grams and kilograms with a measuring scale. For example, when you make a cake, you measure the mass of the flour, sugar, and butter in grams on a measuring scale.
How to Measure Weight
We measure weight in Newtons on a forcemeter. The forcemeter hangs by a hook and has a hook at the other end to hang what you are measuring.
Let’s Investigate!
Question: How can we measure the mass and weight of objects?
Equipment: A scale to measure mass and a forcemeter to measure weight, a plastic carrier bag, and objects of different masses to measure.
Method:
- Draw a table to record your measurements. You will need a column for the objects, a column for the mass of the objects in grams, and a column for the weight of the objects in newtons.
- Place each object on the scale, one at a time. Record your measurements on your table.
- Hold the forcemeter by the top hook. Put each of the objects in the plastic bag, one at a time. Hang the bag on the bottom hook of the forcemeter. Record your measurements on your table.
Follow-up Questions:
Tap to See Answers
- 1: The pattern shows that weight and mass are related but not the same. Mass is constant, while weight changes with gravity.
- 2: Some measurements might be different if the object was not placed properly on the scale or forcemeter. Rechecking helps ensure accuracy.
- 3: One kilogram of any object on Earth has a weight of 9.8 newtons.
- 4:
- a. The mass would be the same because mass does not change, but the weight would be different due to lower gravity on the Moon.
- b. The weight would be less on the Moon because the gravitational pull is weaker.
What is Weightlessness?
When you are in space, the main thing to get used to is zero gravity. The International Space Station (ISS) is permanently in orbit around the Earth. Scientists from many countries visit the Space Station to carry out research in space. The Space Station is attracted by gravity to the Earth. Its forward motion just about equals the speed of its 'fall' toward the Earth.
Astronauts Experience Weightlessness
Astronauts inside the Space Station are not pulled in any particular direction, so they float, meaning that they have a feeling of weightlessness. Floating might sound relaxing, but it is not good for your bones and muscles to float for a long time! Weightlessness causes several systems of the body to relax, because it is no longer fighting the pull of gravity.
Space Flight Effects on the Body
For example, astronauts experience difficulty in determining where their arms and legs are located in space. One astronaut said, “The first night in space when I was drifting off to sleep I suddenly realized that I had lost track of my arms and legs. For all my mind could tell, my limbs were not there.”
Astronaut Health in Space
Astronauts in space for weeks to months can get more health problems. Calcium in their bones is lost through their urine. This causes their bones to weaken. They are more likely to break their bones if they slip and fall.
Rehabilitation After Space Flight
Astronauts’ muscles become weak in space. They have to exercise for two hours a day in space to try to overcome these effects. Exercising is quite difficult to do in such a small space. In spite of this exercise, after a typical six-month space mission, astronauts need several months of rehabilitation when they return to Earth. During this period of rehabilitation, they re-train their bodies to live on Earth and re-build their strength.