MECHANICS Flashcards
Scalar
a quantity with no direction and has magnitude
Vector
a quantity with magnitude and direction
name examples of scalars
- length/distance
- speed
- mass
- temperature
- time
- energy
name examples of vectors
- displacement
- velocity
- force
- acceleration
- momentum
Moment
the turning effect of a force around a turning point
What does a moment of a force depend on
- size of the force
- how far the force is applied from the turning point
equation for moments
moment (Nm) = force (N) * distance (m)
what is the principle of moments
for a body to be in equilibrium, the sum of clockwise moments about any point equals the sum of the anticlockwise moments about the same point.
couples
a pair of forces of equal size which act parallel to each other, but in opposite directions.
centre of mass
the single point that you consider its whole length can act through (whatever its orientation).
- the object will balance around this point
How to find the centre of mass by experiment
- Hang the object freely from a point
- Draw a vertical line downwards from the point of suspension - use a plumb bob to get your line exactly vertical
- Hang the object from a different point and draw another vertical line
- The centre of mass is where the two lines cross
Speed
how fast something is moving regardless of direction
displacement
how far an objects travelled from its starting point in a given direction
velocity
the rate of change of an objects displacement (its speed in a given direction)
acceleration
the rate of change of an objects velocity
what does the gradient (curved) show in a displacement time graph
acceleration
what does the gradient (straight line) show in a displacement time graph
velocity
what does the gradient show in a displacement time graph
acceleration
Drag forces
forces that oppose the motion of an object moving through a fluid (gas or liquid)
Properties of drag forces
-Are always in the opposite direction to the motion of the object
-Never speed an object up or start them moving
-Slow down an object or keeps them moving at a constant speed
-Convert kinetic energy into heat and sound
Lift
an upwards force on an object moving through a fluid. It is perpendicular to the fluid flow
Describe the forces acting on a skydiver
-their velocity increases due to the downward force of their weight
-the increase in velocity means air resistance also increases and acceleration decreases
-eventually the skydiver reaches velocity where their weight equals the force of air resistance
-acceleration is 0 = terminal velocity
Newton’s First Law
An object will remain at rest or move with constant velocity unless acted on by a resultant force
Newton’s Second Law
The resultant force acting on an object with a constant mass is directly proportional to its acceleration
F = ma
Newton’s Third Law
If Object A exerts a force on Object B, then Object B will exert a force on Object A which is equal in magnitude but opposite in direction
A Newton’s third law force pair must be:
-The same type of force
-The same magnitude
-Opposite in direction
-Acting on different objects
Linear momentum
the momentum of an object that is moving in only one dimension
The Principle of Conservation of Momentum
The total momentum before a collision is equal to the total momentum after a collision, provided no external force acts
