Calculating centripetal force
- Centripetal force can be calculated using the equations:
- Centripetal force and linear velocity, v
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- Centripetal force and angular velocity, ω
- Where:
- = magnitude of the centripetal force, measured in newtons (N)
- = mass of object, measured in kilograms (kg)
- = velocity, measured in meters per second (m s-1)
- = radius of orbit, measured in meters (m)
- = angular velocity measured in radians per second (rad s-1)
- These two equations for centripetal force are equivalent because of the equation linking linear and angular velocity
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- Substituting into the first centripetal force equation
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- Simplify the equation
Centripetal force
Centripetal force is always perpendicular to the direction of travel
Worked example
A bucket of mass 8.0 kg is filled with water is attached to a string of length 0.5 m.
What is the minimum speed the bucket must have at the top of the circle so no water spills out?
Answer:
Step 1: Draw the forces on the bucket at the top
Step 2: Calculate the centripetal force
- The weight of the bucket = mg
- This is equal to the centripetal force since it is directed towards the centre of the circle
Step 3: Rearrange for velocity v
- m cancels from both sides
Step 4: Substitute in values