4.1 Forces, Density, Pressure Flashcards
1
Q
Force
A
Rate of change of momentum
2
Q
Density
A
Mass per unit of volume of a substance
3
Q
Pressure
A
Force per unit area
4
Q
Finding resultant (nose to tail)
A
- By accurate scale drawing
- Using trigonometry
5
Q
Forces on masses in gravitational fields
A
A region of space in which a mass experiences an (attractive) force due to the presence of another mass.
6
Q
Forces on charge in electric fields
A
A region of space where a charge experiences an (attractive or repulsive) force due to the presence of another charge
7
Q
Upthrust
A
An upward force exerted by a fluid on a submerged or floating object
8
Q
Origin of Upthrust
A
- Pressure on Bottom Surface > Pressure on Top Surface
- ∴ Force on Bottom Surface > Force on Top Surface
- ⇒ Resultant force upwards
9
Q
Frictional force
A
- Force that arises when two surfaces rub
- Always opposes relative or attempted motion
- Always acts along a surface
- Value varies up to a maximum value
10
Q
Viscous forces
A
- A force that opposes the motion of an object in a fluid
- Only exists when there is motion.
- Its magnitude increases with the speed of the object
11
Q
Centre of gravity
A
Point through which the entire weight of the object may be considered to act
12
Q
Couple
A
A pair of forces which produce rotation only
13
Q
To form a couple
A
- Equal in magnitude
- Parallel but in opposite directions
- Separated by a distance dd
14
Q
Moment of a Force
A
- Product of the force and the perpendicular distance of its line of action to the pivot
- Moment = Force × ⊥Distance from Pivot
15
Q
Torque of a Couple
A
- The product of one of the forces of the couple and the perpendicular distance between the lines of action of the forces.
- Torque = Force × ⊥Distance between Forces
