Mechanics Flashcards
What is mechanics?
The study of motion and forces
What is kinematics?
The study of motion only
[it does not take into account the forces acting on it nor it’s effects ; eg when a question says: ‘ignoring air resistance, calculate …’ ]
[object has to be moving]
What is dynamics?
The study of both forces and motion of an object
[object has to be moving]
What is statics?
The study of forces ONLY, acting on a stationary object
[can’t take into account motion anyways coz object is not moving]
What are the 5 ‘speeds’ that an object can travel at?
- At rest
- Constant Speed
- Constant Velocity
- Constant acceleration
- Changing acceleration
What is velocity?
A vector quantity ; Speed (as its magnitude) in a certain direction
What does it mean for an object to be at constant velocity?
It means that both speed and direction are constant (don’t change)
[therefore, if an object was to travel a circular path at a constant speed , velocity would still not be considered constant because direction it’s travelling changes; applies to acceleration too coz acceleration is the rate of change of velocity]
What does it mean if the velocity of an object is not constant?
It means either the speed is changing or the direction the object is travelling in changes.
[ Since acceleration is the rate of CHANGE IN VELOCITY, this means that if one of these factors changes then it not only means velocity is not constant but also acceleration. Therefore, if velocity is changing then it has acceleration, if it’s not changing then it has zero acceleration]
What is acceleration?
A vector quantity; The rate of change in velocity
What does it mean for an object to have constant acceleration?
It means velocity is changing at the same rate for any given interval
[eg the velocity of a car increasing by 2m/s every second]
What does it mean for an object to have changing acceleration?
It means velocity is changing at different rates for each given interval
[eg the acceleration of a car: 1st second, velocity= 20m/s, 2nd second: velocity = 23m/s , 3rd second: velocity = 30m/s]
What is another word that can be used instead of constant?
Uniform- When something is uniform, it is unchanging; stays the same
Where is the centre of mass in a uniform object?
The centre of the object
Where is the centre of mass in a non-uniform object?
idk cl
What are the 3 types of motion?
- Linear motion
- Projectile motion
- Rotational motion
[Projectile motion can also be referred to as parabolic motion because the shape of the motion the object makes a parabola]
[Rotational motion = moments]
What is linear motion?
When an object only travels in one direction ; a straight line
[it is still considered linear motion if the object travels back and forth along the ‘line’}
What are moments?
A moment is the turning effect of a force about a fixed point
[the turn can either be clockwise or anti-clockwise and this has to be stated in questions]
[torque and moment is the same thing; just usually used in different contexts]
What is a pivot and how does it work?
The fixed point that an object rotates about in a moment. When the object rotates, the pivot doesn’t move.
- The closer you get to the pivot, the more force that has to be applied to produce a turning effect (moment). If you applied that same force along the pivot then the moment = zero ; sometimes referred to as line of action going through/along pivot
- However, if you were to apply that same force further away from the pivot there would be a bigger turning effect
[ Real-life example: make the middle of the pen the pivot and apply forces]
How can a moment be calculated?
Multiply the magnitude of the force, by the perpendicular distance between line of action to the pivot
What is a zero moment?
When a body/object does not rotate because the moments are balanced
What are the conditions for a moment to happen?
- An external force must be applied ; Without a force acting on the object, there won’t be any turning effect (moment).
- The Force Must Not Act Through the Pivot Point ; If the force passes through the pivot, it doesn’t create any turning effect, since the distance from the pivot point to the line of action of the force would be zero ; There Must Be a Perpendicular Distance
What is a couple?
A pair of equal forces acting in opposite directions
How do moments work in a couple (in relation to forces)?
- It is calculated by multiplying the magnitude of either force (F) by the distance between them (s) or (d)
- This moment results in pure rotation without any linear motion because forces in a couple cancel out in terms of net force (i.e., there’s no overall translational motion because F = 0N), instead they produce rotational motion due to the turning effect.
Example:
[Imagine a door with two forces applied on opposite sides. If you push the door with one hand to the right at the top and another force applied in the opposite direction at the bottom, this would create a couple. Both forces would be equal in size but opposite in direction, and the distance between the forces would be the height of the door (if forces are applied at the top and bottom). The resulting moment would rotate the door.]
If a body is in equilibrium then what does it mean about its forces and moment? [3]
-Resultant force = 0N
-Resultant moment = 0Nm
-Moments acting clockwise = moments acting anti-clockwise
