CRITICAL THINKING: The term ”weight” in physics has the following very specific meaning:
“The weight of an object is the name given to a particular force: the gravitational force exerted by the earth on the object, giving it an acceleration of 9.8 m/s2 near the surface of Earth.”
In ordinary speech the use of “weight” is nowhere nearly so precise. What, if anything, is wrong with the following statements? Explain, and correct the statements to become scientifically accurate if they are incorrect.
a) A 3-kg object has a weight of about 30 N at the surface of Earth.
b) A 120-lb person weighs about 55 kg.
c) An astronaut orbiting Earth experiences weightlessness
d) If you eat too much you may gain weight.
a) the earth exerts a force called gravitational force on every particle on its surface.. The force of gravity has a value of 9.8 or 10 meters per second square when approximated . Also weight is the product of the mass of the object by the downward force acting on it (gravitational force)... So [ 3Kg * 10 m/s2 = 30 Newton ]
a) A 3-kg object has a weight of about 30 N at the surface of Earth.
The statement is incorrect. Weight is a force, and its magnitude is given by the product of mass and acceleration due to gravity. The weight of an object can be calculated using the formula:
Weight = mass x acceleration due to gravity.
On the surface of the Earth, the acceleration due to gravity is approximately 9.8 m/s^2. Therefore, to find the weight of a 3 kg object, we can calculate:
Weight = 3 kg x 9.8 m/s^2 = 29.4 N (approximately).
So, the correct statement would be: A 3-kg object has a weight of about 29.4 N at the surface of Earth.
b) A 120-lb person weighs about 55 kg.
The statement is incorrect. The conversion between pounds (lb) and kilograms (kg) is not accurate. To convert pounds to kilograms, we need to multiply the number of pounds by the conversion factor of 0.4536 kg/lb.
To determine the weight of a person in kilograms, a correct conversion would be:
Weight (kg) = 120 lb x 0.4536 kg/lb = 54.43 kg (approximately).
So, the corrected statement would be: A 120-lb person weighs about 54.43 kg.
c) An astronaut orbiting Earth experiences weightlessness.
The statement is correct. When an astronaut is in orbit around Earth, they experience a sensation of weightlessness. This is because they are actually falling freely around the Earth, under the effect of gravity, but their spacecraft and everything inside it is also falling with the same acceleration. As a result, there is no contact force between the astronaut and the spacecraft, giving the perception of weightlessness.
d) If you eat too much, you may gain weight.
The statement is correct. In ordinary speech, the term "weight" is often used to refer to the measure of the heaviness or mass of an object or body. In the context of human health, eating an excess of calories can lead to weight gain. This is because the body stores excess calories as fat, which increases the overall mass and weight of the person.