# What about Newton's second law of motion

## Strength and change of movement

#### 2. Newton's law - principle of action

You can formulate the principle of action linguistically with:

If a resulting force acts on a body of mass, the body is accelerated in the direction of the acting force. Here \ (\ vec {F} = m \ cdot \ vec {a} \) applies.

With the help of the relation \ (\ vec {a} = \ frac {\ Delta \ vec {v}} {\ Delta t} \) you can also use the force law with \ [\ vec {F} = m \ cdot \ vec {a} = m \ cdot \ frac {\ Delta \ vec {v}} {\ Delta t} \]. This is helpful because, unlike accelerations, we can often simply measure times and speeds.

Danger: You must not deduce from the principle of action that the body also moves in the direction of the force or acceleration. This is the case if the body was previously at rest, but mostly not if the body is already moving. For example, if a car rolls over the edge of a table, a resultant force acts on the car vertically in the direction of the floor, but it does not move vertically downwards, but at an angle (parabolic). The resulting acceleration \ (\ vec {a} \) and the resulting speed \ (\ vec {v} \) do not point in the same direction here.

#### Special case 1. Newton's law

If you look closely, Newton's 2nd law also includes Newton's 1st law. If there is no resulting force acting on a body, the body is not accelerated and thus performs a linear, uniform movement. This corresponds to the statement of Newton's 1st law. There are historical reasons that both laws are usually formulated separately.