← Uniform circular motion

Calculate centripetal acceleration

A car holds a steady 10 m/s around a flat circular curve of radius 20 m.

What is its centripetal acceleration?

Start with the car's own numbers: v = 10 m/s, r = 20 m.

Square the speed, and divide by the radius: (10 × 10) / 20 = 5. The car's centripetal acceleration is 5 m/s².

That move is the equation you have seen: a = v²/r.

Finding a centripetal acceleration is a routine, and the same three steps work every time.

Step 1: write down the values in the question, and mark the unknown.

Step 1: the values, unknown markedquantityvaluev10 m/sr20 ma?
Step 1: write down the values, and mark the unknown.

Step 2: write down the equation.

Step 3: substitute in the values, and calculate. The result line always carries its unit: m/s².

Steps 2 and 3: equation, then substitutionsteplineequationa = v²/rsubstitutea = (10 × 10) / 20resulta = 5 m/s²
Steps 2 and 3: the equation, then a = 5 m/s².

Every case here is steady-speed circular motion: v is the steady speed, and r is the circle's radius.

A car holds a steady 10 m/s around a flat circular curve of radius 20 m. Calculate its centripetal acceleration.

Write down the values:

v = 10 m/s, r = 20 m, a = ?

Write down the equation:

a = v²/r

Substitute in the values, and calculate:

a = (10 × 10) / 20 = 5

The car's centripetal acceleration is 5 m/s².

A passenger train takes a wide circular curve of radius 300 m at a steady 30 m/s. Calculate its centripetal acceleration.

Write down the values:

v = 30 m/s, r = 300 m, a = ?

Write down the equation:

a = v²/r

Substitute in the values, and calculate:

a = (30 × 30) / 300 = 3

The train's centripetal acceleration is 3 m/s².

Quick-fire drill

A remote-control car circles a flat loop of radius 4 m at a steady 6 m/s. Enter its centripetal acceleration in m/s².

A car rounds a flat traffic circle of radius 30 m at a steady 12 m/s. Enter its centripetal acceleration in m/s².

A go-kart holds a steady 16 m/s around a flat circular corner of radius 32 m. Enter its centripetal acceleration in m/s².

A motorcycle rounds a flat circular bend of radius 50 m at a steady 15 m/s. Enter its centripetal acceleration in m/s².

A sports car laps a flat circular test pad of radius 45 m at a steady 18 m/s. Enter its centripetal acceleration in m/s².

A track cyclist holds a steady 14 m/s around a flat circular course of radius 28 m. Enter her centripetal acceleration in m/s².

Your turn

A horse gallops a circular training ring of radius 22 m at a steady 11 m/s. Enter its centripetal acceleration in m/s².

A bus takes a flat circular highway ramp of radius 65 m at a steady 13 m/s. Enter its centripetal acceleration in m/s².

A car joins a long, flat highway curve that forms part of a circle of radius 160 m. Its cruise control holds a steady 24 m/s the whole way around the curve. Enter its centripetal acceleration in m/s².