## IB Physics Glossary

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### S

occurs when a satellite moves into a low orbit such that the frictional force increases the speed of the satellite.

 "As an artificial satellite gradually descends in a near-circular orbit, its linear velocity increases. Its acceleration in the direction of its motion is found to be the same as if the air drag force, reversed, were pushing the satellite.

 Keyword(s): 9.4

#### Scalar multiplication

of vectors, changes the magnitude of the vector but not the direction.
For scalar $$a$$ and vector $$\vec{A}$$ with
x- or horizontal component $$A_H=A \cos \theta$$
y- or vertical compnonet $$A_V= A \sin \theta$$
magnitude $$A=\sqrt{A_H^2 + A_V^2}$$

The multiplication $$a \times \vec{A}$$ has magnitude $$a \times A$$.
The division $$\vec{A} \div a$$ has magnitude $$A \div a$$.
 Keyword(s): 1.3

#### Scalar quantities

have magnitude only. Direction or changes in direction have no effect on scalar quantities. Examples include distance, speed, mass and temperature.
 Keyword(s): 1.3

#### Schönberg-Chandrsekhar limit

states, a star leaves the main sequence when it consumes about 12% of its hydrogen fuel. (d)
 Keyword(s): E5

is the distance from the centre of a black hole at which the escape velocity is equal to the speed of light in empty space, c. The radius can be found using
$$R= R_s = \frac{2GM}{c^2}$$
where G is the gravitational constant, M is the mass of the black hole and c is the velocity of light in empty space.
 Keyword(s): 9.4, E5

#### Scotopic vision

is black and white vision which occurs in low-light conditions. Vision is aided by the rod cells. Cone cells don't play a role.
 Keyword(s): A1

#### Second law of thermodynamics

states that

thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temperature

or

the total entropy of the universe must always stay the same or increase.
 Keyword(s): 10.2

#### Secondary colors

are Cyan (Blue & Green), Magenta (Blue & Red) and Yellow (Green and Red).
 Keyword(s): A1

#### Sensory hearing loss

occurs when the air conduction thresholds (middle ear) and the bone conduction thresholds (cochlea) both show a hearing losses. If bone conduction losses are greater than a cochlea implant may be required. Reasons include

1. ageing;
2. prolonged exposure to excessive noise.
 Keyword(s): I1

#### Signifiant figures

a rule, the number of significant digits in a result should not exceed that
of the least precise value upon which it depends.
 Keyword(s): 1.2

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