P6: Forces in Action Flashcards
The Centre of Mass
The point on an object at which its mass may be thought to be concentrated.
Where is the centre of mass on a symmetrical object?
Where its axis of symmetry cross.
Test for the centre of mass of a thin sheet of material.
- Suspend the material from a stand.
- Use a ‘plumbline’ to draw a vertical line from the rod downwards.
- Repeat this process from a second point- the centre of mass will be where the two lines cross.
Oscillating Motion
Motion of any object that moves to and fro along the same line.
Simple Pendulum
A pendulum made up of a small spherical bob suspended by a string from a fixed point.
The Amplitude of an Oscillating Object:
The distance an object moves from its equilibrium position to its higher position on either side.
For a pendulum, the frequency of the oscillations is…
… the number of complete cycles of oscillation per second. (measured in Hz)
(Pendulums)
The time period (s) =
1/ Frequency of the oscillations (Hz)
Moment
The turning effect of a force.
Moments equation
Moment (nm) =
Force (n) x Perpendicular distance from the line of action of the force to the pivot (m)
When using a lever, the weight of an object is called a __, and the force a person applies is called the __.
The point around which the crowbar turns is called the __ or the __.
Load
Effort
Pivot
Fulcrum
Force Multiplier
A lever used so that a weight or force can be moved by a smaller force than it could previously.
Line of Action
The line along which a force acts.
The Principle of Moments
The sum of all the clockwise moments around a point
The sum of all the anticlockwise moments around a point
When is an object stable?
When its line of action remains within its base.
When is an object unstable?
When its line of action strays from inside the base.
How is an object’s stability increased?
By widening the base
Resulting Moment
The difference between the sum of the clockwise moments and the sum of the anticlockwise moments about the same point if they are not equal.
When will an object topple over?
If the resultant moment around an object’s turning point is not 0.
Centripetal Acceleration
The acceleration of an object moving around in a circle towards the centre of the circle.
Centripetal Force
The resultant force towards the centre of a circle acting on an object moving in a circular path. This is what causes the centripetal acceleration.
What is significant about the velocity of an object moving at a constant speed in a circle?
The velocity is constantly changing because the objects direction is always changing.
What does the centripetal force of an object depend on?
> Mass
Speed
Radius of the Circle
Pressure (Pa or N/m(2)) =
Force/ Area
