How does this relate to Newton's second law?
It is Newton's second law, stated as F = ma: the net force on an object equals its mass multiplied by its acceleration. Rearranged, a = F/m tells you how fast something speeds up under a known push, and m = F/a gives mass from a measured force and acceleration. The law only applies to the net force — the vector sum of everything acting on the object — so competing forces have to be resolved first. Where the net force is zero the acceleration is zero, which is Newton's first law falling out as a special case.
What is Newton's second law?
Force equals mass times acceleration — F = ma. A newton is the force that accelerates one kilogram at one metre per second squared. The law is why the same push moves a shopping trolley easily and a car barely at all: for a given force, acceleration falls as mass rises. It also means force is required to *change* motion, not to maintain it, which is the part that contradicts everyday intuition.
What is the difference between mass and weight?
Mass is how much matter an object contains, measured in kilograms, and it does not change with location. Weight is the force gravity exerts on that mass — mass times gravitational acceleration — measured in newtons. A 70 kg person weighs about 686 N on Earth but roughly 113 N on the Moon, while their mass is 70 kg in both places. Bathroom scales report mass but are calibrated assuming Earth's gravity.
Why is the newton such a small unit?
Because one newton is only about the weight of a small apple — 102 grams. Everyday forces are therefore large numbers: a 70 kg person standing still exerts 686 N on the floor, and a car braking hard generates several thousand. Engineers commonly work in kilonewtons for structural loads. The unit is small because it derives from base SI units rather than from anything human-scaled.
How do multiple forces combine?
As vectors, not simple sums. Two forces in the same direction add; opposing forces subtract; forces at an angle combine using components or the parallelogram rule. The net force determines the acceleration. This is why an object can have several large forces acting on it and not accelerate at all — a book on a table has gravity pulling down and the table pushing up in balance, netting zero.
What is the relationship between force, impulse and momentum?
Force applied over time changes momentum, and that product is impulse. The same change in momentum can come from a large force briefly or a small force for longer — which is the entire principle behind crumple zones, airbags and landing with bent knees. They extend the stopping time, reducing the peak force for the same overall change in motion.
Does F = ma always hold?
For everyday situations, yes. It breaks down at speeds approaching light, where relativistic mass increase means force produces less acceleration than expected, and at atomic scales where quantum mechanics governs. It also assumes constant mass — a rocket burning fuel loses mass as it accelerates, so the more general form uses rate of change of momentum instead. For anything you can push by hand, F = ma is exact enough.