TOPIC 4: FORCES Flashcards
[Definition] Field of force
A region of space where a particle experiences a force
[Definition] Gravitational field
A region of space in which a gravitational force acts on a mass
[Definition] Electric field
A region of space in which an electric force acts on a stationary charge
[Definition] Magnetic field
A region of space in which a magnetic force acts on a current-carrying conductor, moving charge, or a permanent magnet
[Definition] Centre of gravity
The point where all the weight of a body seems to act on
Free body diagram VS Labelled force diagram
Labelled force diagram requires specific labelling of ALL forces (e.g. normal contact force by table on mass)
Main forces in the chapter
- Normal contact force
- Weight
- Friction
- Lift / Upthrust
- Tension & Compression
- CONTACT/REACTION FORCE (NOT NCF !!!)
- It is the vector sum of ALL the forces at the contact surfaces
[Definition] Hooke’s Law
Hooke’s law states that the change in length of a material is directly proportional to the force applied on it, provided that the limit of proportionality is not exceeded.
[Formula] Hooke’s Law
F = kx
F: Force applied (N)
k: Proportionality constant (Nm^-1)
x: Change in length (m)
[Definition] Elastic limit
The point beyond which the spring does not return to its original length when the force is removed
[Definition] Pressure
Pressure is defined as the force per unit area.
[Formula] Pressure
p = F/A
p = hpg
What is upthrust equals to?
Weight of fluid displaced
Condition for translational equilibrium
No resultant force
Condition for rotational equilibrium
No resultant torque about any point
[Definition] Principle of moments
Principle of moments states that for a body in rotational equilibrium, the sum of the clockwise moments about any point is equals to the sum of anti-clockwise moments about the same point
[Definition] Moment of a force
Moment of a force about a point is the product of the force and its perpendicular distance to the pivot
[Formula] Moment of a force
M = Fd
[Definition] Torque of a couple
Torque of a couple is the product of one of the forces and the perpendicular distance between the forces
[Definition] Equilibrium
A body is in equilibrium when there is no resultant force and there is no resultant torque about any point on it.
Equilibrium can also be known as dynamic equilibrium / total mechanic equilibrium
Impt things to note:
- Draw labelled force diagram to better answer the question!!!
- Even if rotational equilibrium, if the force is slanted, need to use the vertical/horizontal component of the force. Can’t just use the slanted force straight
