Terminal Velocity

In I/GCSE Physics, an object moving through the air experiences air resistance or drag. The size of this depends on the object’s **shape and speed**. Objects falling through the air experiences two significant forces: **weight and drag**.

When an object has just been released, there is a starting velocity of **0m/s**. This means there is **no drag**. The resulting **downward acting force** is just the **weight force of the Earth**.

When it starts moving, it has a drag force acting against it, m. As the object is** accelerating**, it is getting **faster**. The** faster the object moves**, the **bigger the drag force is**.

The object then reaches a point where the **drag force exactly balances the weight force**. Acceleration is now at zero and the falling object is moving a constant speed. The object has reached **terminal velocity **as stated in the I/GCSE physcis curriculum.

When a **skydiver** jumps off the plane, she will **accelerate **until she reaches terminal velocity. When her parachute opens, it will cause a sudden increase in drag force. This means that there will be an unbalanced force acting upwards, causing her to decelerate. As she **slows down**, the drag force **decreases** and a **new terminal velocity** is reached.

Thinking Distance and Braking Distance

In I/GCSE physics, by definition, thinking distance is the **time taken for the driver to respond or react**. This can be increased if the driver is tired, under the influence of alcohol/drugs or there is poor visibility.

**Braking distance** is the distance taken for the **vehicle to decelerate to rest after the driver has hit the brakes**. This can be increased if the road is slippery or the tyres are screwed up.

Vehicles with a **larger mass** will have **smaller rates of deceleration** as you can see in **F = ma**

Rearranging the equation gives **a = F/m**. If the braking force of two cars, one that weighs 1000kg and one that weighs 1500kg for example, then the car with the bigger mass will come to rest at a longer time than the other car.

Similarly if a car is breaking from **higher velocity**, it takes **longer to stop**

End of this topic!