**Movement in a circle and centripetal force**

**Galileo** - Everybody continues to move with a constant speed unless acted on by a **resultant force**.

From this **Newton** established his first law of motion.

An object that is moving in a circle is said to be accelerating, even if there is no speed change, because the **velocity** is constantly changing.

In GCSE physics curriculum, a net inward force is needed to provide this acceleration. This** 'centripetal' force**, f, always acts towards the centre of the circle and is given by:

**F=ma**

As an object is travelling at a **constant speed** in a circle, the centripetal force acts at r**ight angles** to the direction in which the object is travelling in at any instant.

In GCSE physics, the **amount** of centripetal force need to keep an object moving in a circle depends on:

- the
**mass**of the object: the larger the mass, the larger the force needed - the
**speed**of the object: the faster the speed, the larger the force needed - the
**radius**of the circle: the smaller the radius, the larger the force needed

The mass is constantly accelerating towards the center, O, with a magnitude (m/s2) given by:

**a = v2/r**

Please be reminded that in GCSE physics curriculum, the speed of the object travelling equates to **diameter/time**.

End of this topic!

Drafted by Gina (Physics)