Question 1

What is the difference between mass and weight?

Accepted Answer

Mass is the amount of matter in an object and does not change with location. Weight is the force gravity exerts on that mass, and it changes with the strength of the gravitational field.

An object with a mass of ten kilograms has that mass on Earth, on the moon, and floating in deep space. Its weight differs in each case: about ninety-eight newtons on Earth, roughly a sixth of that on the moon, and effectively nothing far from any large body.

The units reflect the distinction. Mass is measured in kilograms; weight, being a force, is properly measured in newtons. Everyday language ignores this, and bathroom scales report kilograms while actually measuring force, which works because Earth's gravity is near enough constant for the conversion to be invisible.

A useful way to feel the difference is inertia. Mass resists changes in motion regardless of gravity. Pushing a heavy crate sideways in orbit is just as hard as on Earth, even though it weighs nothing, because you are fighting its mass rather than its weight. Astronauts describe exactly this.

This also explains why astronauts on the space station are not weightless because they have escaped gravity. Gravity at that altitude is nearly as strong as at the surface. They appear weightless because they are in continuous free fall around the planet, falling at the same rate as their spacecraft, so nothing pushes back against them.

The practical consequence is that a balance scale, comparing against known masses, gives the same reading anywhere, while a spring scale, measuring force, does not.

Question 2

Why do astronauts float if there is still gravity in orbit?

Accepted Answer

Because they are falling — continuously — and so is everything around them. The common phrase "zero gravity" is simply wrong about the physics. Gravity at the International Space Station is roughly

Question 3

What are the SI units actually based on now?

Accepted Answer

Since a redefinition that took effect in 2019, all seven base units are defined by fixing the numerical values of physical constants — not by physical objects, and not by properties of materials. It

Question 4

What are the basic concepts I need to understand in physics?

Accepted Answer

Basic concepts in physics include matter, energy, force, motion, gravity, waves, and thermodynamics. These fundamentals are essential for understanding advanced physics topics and their applications.

Question 5

What is statistical power, and why do underpowered studies mislead?

Accepted Answer

Power is the probability that a study will detect an effect if one genuinely exists. Low power means a real effect is likely to be missed — and, far less intuitively, it also makes the findings that

Question 6

What is an effect size, and why does it matter more than significance?

Accepted Answer

A measure of how large a difference or relationship is, expressed in a standardised or interpretable form — and it answers the question significance testing does not: not whether an effect exists,

Question 7

What are the key concepts of electricity that beginners need to grasp?

Accepted Answer

Understanding electricity basics is vital for grasping how electrical systems work. Key concepts include voltage, current, resistance, and power, which are foundational for practical applications.

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