5.2 Circular Motion Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

what is one radian defined as?

A

one radian is defined as the angle subtended at the centre of a circle when the arc length is equal in length to the radius of the circle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is 2π radians equal to?

A

360° (a full circle)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define frequency

A

no. of complete revolutions per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define period

A

the time period is the time taken in seconds for one complete circular path

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is angular velocity ω?

A

the rate of angular rotation measured in radians per second, rad s^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the angular velocity formula? (ω)

A

ω = 2π / T or ω = 2πf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the formula for constant linear speed in a circle?

A

v = ωr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how do you get to the constant linear speed in a circle equation?

A

V = d / t
V = 2πr / t
subbing in ω = 2π / T gives you…
v = ωr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

are objects travelling in circles accelerating?

A

yes since their velocity is changing because their direction is changing (actual speed in a circle is constant) and acceleration is defined as the rate of change of velocity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is centripetal acceleration?

A

the acceleration of an object moving in a circle and it is always defined directed towards the centre of the circle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is a key point about circular motion in terms of acceleration and velocity?

A

there is no acceleration parallel to the direction of motion, velocity remains perpendicular to the direction of the force/acceleration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the formula for centripetal acceleration?

A
a = v^2 / r
a = ω^2 x r (since v = ωr)
where a = centripetal acceleration
v = linear velocity
ω = angular velocity
r = radius
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the name of the force that keeps something moving in a circle?

A

centripetal force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the definition of centripetal force?

A

the centripetal force is the resultant force on an object acting towards the centre of the circle, causing it to move in a circular path

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

in what direction does the centripetal force and acceleration act?

A

radially inwards towards the centre of the circle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the formula for centripetal force?

A
F = mv^2 / r
or F = mω^2r
where m = mass
v = velocity
r = radius of the circle
17
Q

why does the speed or KE of the object in circular motion stay constant?

A

although the force changes the direction of motion, the object’s velocity remains perpendicular to the direction of the force, the object never moves towards or away from the circle, so there is no motion in the direction of the force, hence no work is done on the object, and the object’s KE (and therefore speed) remains constant

18
Q

what is the type of centripetal force acting when a car is travelling around a roundabout?

A

frictional force

19
Q

what is the type of centripetal force acting when a satellite is orbiting Earth?

A

gravitational force

20
Q

what is the type of centripetal force acting when a electron orbits the nucleus of an atom?

A

electromagnetic force

21
Q

what is the type of centripetal force acting when a rubber bung is being spun around on a string?

A

force of tension

22
Q

in a conical pendulum is the ball in equilibrium?

A

the ball is in equilibrium vertically but there is a resultant force on the ball directed horizontally towards the centre of the circle (the horizontal component must accelerate the ball towards the centre of the circle)
vertical component of tension T = weight of the ball

23
Q

what is the equation linked to the conical pendulum?

A
tanθ = v^2 / Rg
where θ = angle from the normal
v = velocity
R = radius of the circle
g = acceleration due to gravity
24
Q

outline an experiment to investigate circular motion using a whirling bung

A
  • tie one end of the thread to rubber bung and make a mark on the string at a distance of 0.3m from the bung
  • attach a 1.0N weight at the other end of the string and whirl the rubber bung in a horizontal circle (wear eye protection)
  • adjust the speed of rotation such that the radius r of the circle is constant and equal to 0.3m and then continue to whirl the bung at a constant speed
  • measure the time, t, for 10 revolutions of the bung
  • determine the speed, v, of the bung using s = d / t since the bung is making 10 revolutions, and the circumference is 2πr, then v = 10 x 2πR / T which simplifies to v = 20πr / t
  • repeat the experiment for different values of centripetal force F by adding masses to the bottom, an adjusting the speed of rotation till the bung whirls in a circle of the same radius as before, record your results in a table
  • plot a graph of force F against v^2, draw a straight LOBF
  • the gradient of the line will be equal to m / r
  • determine the mass of the bung from the gradient and the value of r used in the investigation (compare with actual mass of bung for validity)
25
Q

when you’ve got roller-coaster carriage spinning on a loop-the-loop roller-coaster where does the passenger feel weightless and why?

A

they feel weightless at the top because the reaction force on them becomes small, because now their weight provides some of the centripetal force inwards the reaction force is smaller
(reaction force is largest at the bottom)