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CIE A Level Maths: Mechanics復習筆記3.3.3 Coefficient of Friction - F = ma

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年8月17日下午5:39

The?coefficient of friction?combined with?F?=?ma?allows you to determine an object's motion where friction is involved in a problem
For problems where the surface is horizontal:

Step 1. If necessary,?resolve?any angled forces into vertical and horizontal components

Step 2. Calculate the normal reaction force?R

- Be careful – if there are vertical forces other than gravity these will affect the value of?R
- with a horizontal surface?R?will always be directed vertically upwards
- the magnitude of?R?will be such as to make the?total?make the?total?vertical force on the object zero

Step 3. Calculate?F_MAX=?μR?and find the?resultant?(total force) of all the horizontal forces on the object

- Remember – if the resultant of the other horizontal forces is less than or equal to?F_MAX?then friction will exactly balance those forces out and the object will remain stationary

Step 4. Use?F = ma?to determine the acceleration of the object

3.3.3_WE_Co-of-Fric-F-ma_1

cie-3-3-3-coefficient-of-friction---fma-worked-solution-1

Always draw a force diagram and label it clearly.Look out for the words?smooth?and?rough?in mechanics problems involving an object moving (or potentially moving) along a surface:
- If the surface is described as?smooth?then you can ignore friction in the problem (ie?μ=?0)
- If the surface is described as?rough?than you need to include the force of friction in solving the problem