Newton's Second Law Flashcards

All 6 cards in this deck

State Newton's Second Law of motion (in words, as a proportionality).

The acceleration of an object is proportional to the resultant force acting on it, and inversely proportional to the mass of the object.

Write down the equation that links resultant force $F$, mass $m$ and acceleration $a$, with the units of each quantity.

resultant force = mass × acceleration, $F = m\,a$ — $F$ in newtons (N), $m$ in kilograms (kg), $a$ in metres per second squared (m/s²).

What are the steps to calculate the acceleration of an object from the resultant force on it?

e.g. a resultant force of $12$ N acts on a mass of $4$ kg

1. Write the equation: $F = m\,a$, so $12 = 4 \times a$
2. Rearrange: $a = F \div m = 12 \div 4$
3. Evaluate: $a = 3$ m/s²

What are the steps to find the resultant force when you are given a change in velocity and a time?

e.g. a $1000$ kg car speeds up from rest to $10$ m/s in $5$ s

1. Find the acceleration: $a = \dfrac{\Delta v}{t} = \dfrac{10}{5} = 2$ m/s²
2. Write $F = m\,a = 1000 \times 2$
3. Evaluate: $F = 2000$ N

What typical values would you use for the mass and acceleration of an ordinary car when estimating the force involved in road transport?

Mass about $1000$ kg and acceleration a few m/s² (roughly $2$ m/s²), giving a force of around $2000$ N.

True or false? In $F = m\,a$, $F$ can be any one of the forces acting on the object.

False. $F$ must be the resultant (net) force of all the forces acting.