Newton's Second Law with Numbers
Treating F = ma as a working equation: the resultant force sets the acceleration, and mass measures how strongly an object resists that change. Mass, not weight, is what appears in the calculation.
What a learner can do afterwards
- Calculates any one of resultant force, mass or acceleration when the other two are given
- Explains why a loaded trolley accelerates less than an empty one under the same push
- Uses the resultant of several forces, not one single force, in the calculation
1 · Read
Newton's second law fits in one line: resultant force equals mass times acceleration. Push twice as hard and you get twice the acceleration. Keep the push the same but double the mass, and the acceleration halves.
Resultant means the single force left after every push and pull is combined, so always combine first and calculate second. Draw the object with every force as an arrow, pick a direction to call positive, then feed the total into F equals m a, with mass in kilograms.
A loaded trolley accelerates less than an empty one under the same push, since more mass resists the change. Friction and drag join the arrows too, so the resultant can be far smaller than the push you apply. Say the forces in words first; if the words make sense, the sum usually follows.
Watch the units and the signs. Mass goes in as kilograms and acceleration comes out in metres per second squared. A quick sketch stops sign mistakes before they happen, especially when friction points against the motion.
Combine forces into one resultant, then let F equals m a do the rest.
More to read
4.3 Newton’s Second Law of Motion: Concept of a System
Newton's second law links force, mass, and acceleration in one neat equation: resultant force equals mass times acceleration. Push twice as hard and you get twice the acceleration. Keep the push the same but double the mass, and the acceleration halves.
The word resultant matters a lot. It means the single force left after every push and pull on the object is combined. Always combine the forces first, then feed that total into the equation.
4.6 Problem-Solving Strategies
Force problems get easy when you work them the same way every time. First draw the object on its own with every force as an arrow. Then pick a direction to call positive and add the arrows up to get the resultant.
Only then do you reach for F = m a. Put the resultant force in, keep mass in kilograms, and the acceleration comes out in metres per second squared. A quick sketch stops sign mistakes before they happen.
4.7 Further Applications of Newton’s Laws of Motion
The same law explains everyday puzzles once you spot the system. A loaded trolley accelerates less than an empty one under the same push because there is more mass for the force to shift. Friction and air resistance join the force arrows too, so the resultant can be much smaller than the push you apply.
Try explaining each example in words before touching numbers. Say which forces act, which way they point, and what the resultant is. If the words make sense, the calculation that follows is usually right.
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2 · Watch
En anglaisTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.