physics revision flashcards p5

8/19/2019 Physics Revision Flashcards P5

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Speed and velocity

To measure the speed of an object, you only need to measure how

fast its going – i.e. 30mph

Velocity is a more useful measure of motion as it describes bothspeed and direction – 30mph due north.

- A uantity li!e speed, that has only a number, is called a

scalar uantity. "calar uantities# speed, mass,

temperature, time, length$- A uantity li!e %elocity, that has a direction is well, is a

%ector uantity.Vector uantities# %elocity, force, displacement,

acceleration, momentum.

&hen you loo! out of a car window, a car that's o%erta!ing youdoesn't loo! li!e its mo%ing fast, but a car going in the opposite

direction seems to whi(( past. )t's all to do with relati%e speed –

how fast something is going, relati%e to its speed. A car going the

Combining velocities and forces

To combine * %ectors, you add them end to end.

+ &ith or against current

)t's easy when the plane or whate%er is ying directly into the

wind or whate%er, or with the wind behind it. /n %ector

diagrams, you just need arrows going bac! and forwards.

Velocity of plane & wind.

A light plane is ying east, its airspeed indicator shows +*0!mh.

it is ying into wind of *0!mh. &hat is its resultant %elocity1

2lane %elocity +*0!mh

&ind %elocity *0!mh

4esultant %elocity +*0-*0 +00!mh


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5rom the ground, itloo!s li!e the plane

tra%els at +00!mh.

)f the plane and

wind were in the

same direction, youadd the %elocities.

* Across the current

A boat is going west at +6ms, in a ri%er with a current running

north at 7ms. &hat is the resultant %elocity1

To wor! out %elocity, you need speed and direction, it's a right

angled triangle so#

Pythagoras: speed

+8.+ms

Trigonometry: direction tan -+ 7+6 *9.:;

Current velocity = 8ms

!oat velocity = "#ms

$esultant velocity = "%."ms &

)


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7


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5orce *

Tan-+ 300600 38.9;

300


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Pro6ectile motion

The path of a projectile is always a parabola.

- A projectile is something that is projected, or dropped, and

from then on, only has earth's gra%itational Beld gra%ity

acting on it ignoring air resistance.

- "o things li!e missiles, golf balls and footballs are all

projectiles.. the path a projectile ta!es through the air

called its trajectory is always parabolic.

- Dow far a ball or other projectile tra%els depends on the

angle its launched at. )t will tra%el furthest if its launched at

6?;.

- )f the angle is less than 6?;, then the projectile wont tra%el

as far.- An angle greater than 6?; means the projectile will ta!e


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7eal with horiontal and vertical motion separately

Era%ity which only acts downwards doesn't aFect hori(ontal

motion at all.

An object projected hori(ontally accelerates %ertically due to

gra%ity , but has no acceleration hori(ontally %elocity stays the

same.

An object can also be projected at an angle, and the motion can

be split into hori(ontal and %ertical parts. Gou can apply this toreal life situations e.g. how far the ball tra%els, depends on the

angle it's struc! at.

- "omething that starts of hori(ontally as a constant

hori(ontal %elocity ignoring frictionair resistance, sincethere are no hori(ontal forces and it's unaFected by

gra%ity.

-

Pro6ectile calculations use e+uations of motions

H


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physics revision flashcards p5

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