Unit 1.1 Basic physics Flashcards
Define quantity.
It is represented by a number multiplied by a unit.
Define pressure.
force / area
State homogeneity rule 1.
Two quantities “a” and “b” can only be added together if they have the same units- and then the answer has the same units. The same goes for subtraction.
State homogeneity rule 2.
An equation is homogeneous only if the units of the two sides are the same.
Define scalar quantity.
Has magnitude only.
Define vector quantity.
Has magnitude and direction.
Define resultant force.
The combined effect of two (or more) forces.
Give the symbol for resultant force.
ΣF (‘sigma F’)
How would you calculate the sum of 2 forces?
Using the parallelogram law of vector addition.
Give 3 ways to find ΣF.
- Drawing a scale diagram
- Using trigonometry
- Pythagoras’ theorem (if the forces are in right angles)
Define mean speed.
distance / time
Define mean velocity.
displacement / time
Define displacement.
A quantity which includes direction as well distance.
Give 3 examples of scalar quantities.
- Density
- Mass
- Volume
Give 3 examples of vector quantities.
- Displacement
- Velocity
- Acceleration
Define resolving.
Finding the component of a force: we resolve a force into its horizontal and vertical components.
Give the formula to work out Fₕ (‘horizontal force’).
Fₕ = F cosθ
Give the formula to work out Fᵥ (‘vertical force’).
Fᵥ = F sinθ
Define density, ρ.
Mass / volume
Give unit for density.
kg m⁻³
How to convert cm³ into m⁻³ ?
1 cm³ = 1 x 10⁻⁶ m⁻³
How to convert kg m⁻³ into g cm⁻³ ?
1000 kg m⁻³ = 1 g cm⁻³
Define moment.
The moment of a force about a point is the product of the force and the perpendicular distance from the point to the line of action of the force.
Give the units for moment.
Nm
Give another name for moment.
Torque
Give 2 types of moment.
- Clockwise moment (CM)
- Anticlockwise moment (ACM)
Give 2 formulas for moment.
- Force * distance (Fd)
- F* xcosθ
State the principle of moments (PoM).
For a body to be in equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about the same point.
Give another condition for a body to be in equilibrium.
The resultant moment about any point is zero.
What is the centre of gravity?
The point at which we can consider all its weight to act.
If an object is moving and rotating at a constant rate, is it in equilibrium?
Yes
Give 2 conditions for an equilibrium.
- The resultant force on the object must be zero.
- The resultant moment (about any point) must be zero.
Give 2 methods to work out 2 unknown forces in a moment question.
- Resolve once and take moments once.
- Take moments about 2 different point.
