Newton's First and Second Laws

**Newton’s first law** says that a resultant force is needed to make something **start moving, speed up** or **slow down**

If the resultant force on a **stationary** object is **zero**, the object will **remain stationary**. If the **resultant force** on a moving object is **zero**, it’ll just carry on moving at the **same velocity**

So when a train or car or bus or anything else is **moving** at a **constant velocity**, the resistive and driving **forces** on it must all be balanced. The velocity will only change if there’s a **non-zero** resultant force actin on the object.

A non-zero

**resultant**force will always produce**acceleration**in the direction of the forceThis

**acceleration**can take**five**different forms:**starting, stopping, speeding up, slowing down and changing direction**On a free diagram, the

**arrows**will be**unequal**

The larger the

**resultant**force acting on an object, the**more**the object**accelerates**-the force and the acceleration are directly proportional. You can write this as F=a**Acceleration**is also**inversely proportional**to the**mass**of the object-so an object with a larger mass will accelerate less than one with a smaller massThere’s a formula that describes Newton’s second law:

**F=ma, Resultant force, mass x acceleration**You can use this to get an idea of the forces involved in everyday

**transport**,**large****forces**are needed to produce large**acceleration**

**Newton’s first law** says that a resultant force is needed to make something **start moving, speed up** or **slow down**

If the resultant force on a **stationary** object is **zero**, the object will **remain stationary**. If the **resultant force** on a moving object is **zero**, it’ll just carry on moving at the **same velocity**

So when a train or car or bus or anything else is **moving** at a **constant velocity**, the resistive and driving **forces** on it must all be balanced. The velocity will only change if there’s a **non-zero** resultant force actin on the object.

A non-zero

**resultant**force will always produce**acceleration**in the direction of the forceThis

**acceleration**can take**five**different forms:**starting, stopping, speeding up, slowing down and changing direction**On a free diagram, the

**arrows**will be**unequal**

The larger the

**resultant**force acting on an object, the**more**the object**accelerates**-the force and the acceleration are directly proportional. You can write this as F=a**Acceleration**is also**inversely proportional**to the**mass**of the object-so an object with a larger mass will accelerate less than one with a smaller massThere’s a formula that describes Newton’s second law:

**F=ma, Resultant force, mass x acceleration**You can use this to get an idea of the forces involved in everyday

**transport**,**large****forces**are needed to produce large**acceleration**