August 1, 2021
Turning effects
- Moment (Nm) = force (N) x perpendicular distance from pivot (m).
- The moment can be increased by increasing the size of the force or using a longer instrument.
- Force applied by a person is called effort.
- The closer to the pivot you are, the harder it will be to lift the load.
Centre of Mass
- Centre of mass = the point of an object where it’s mass is thought to be concentrated.
- In symmetrical objects, the centre of mass is along the lines of symmetry or where the lines of symmetry meet.
- A hanging object rests with it’s centre of mass directly below the point of suspension.
- This is called being in equilibrium.
Balanced moments
- For objects in equilibrium, the total clockwise moment is equal to the total anticlockwise moment.
- To work out this weight, we do 0.3 x 2 = 0.6
- Then, 0.6/0.4 = 1.5N.
- You can also use this to work out unknown distances.
Stability
- Stable objects usually have a wide base and a very low centre of mass.
- When the line of action of weight lies outside the base of an object, it will topple over.
- When the line of action of weight lies inside the base of an object, it shouldn’t topple over.
- Buses and coaches have to take special tests which make sure they do not topple over too easily.
Circular motion
For any object moving in a circle at constant speed:
- Its velocity is directed along a tangent to the circle of direction.
- The velocity constantly changes direction as it moves around the circle.
- The change of velocity is towards the centre of the circle.
- Therefore the object is constantly accelerating towards the centre of the circle.
- The force that acts towards the centre of the circle is called the centripetal force.
Make sure you understand the concepts well as these are very important in I/GCSE Physics! 👨🏫
Centripetal force
Factors that increase centripetal force:
- Decreased radius of the circle e.g. a ball being swung around in a circle on a SHORT piece of string.
- Increased mass of object e.g. a LARGER ball being swung around in a circle on a short piece of string.
- Basically, the larger and further away the object is, the larger the centripetal force will be.
Gravitational forces
Gravity is:
- An attractive force.
- Gets bigger with the mass of each object.
- Gets smaller when the objects get further away from each other.
- As an object leaves the Earth’s atmosphere, the gravitational force acting on it due to the Earth decreases and the gravitational force acting on it due to the moon increases.
References:
http://hyperphysics.phy-astr.gsu.edu/hbase/cm.html
https://commons.wikimedia.org/wiki/File:Circular_motion_velocity_and_acceleration.svg
https://en.wikipedia.org/wiki/Centripetal_force
This is the end of the topic!
Drafted by Cherry (Chemistry)