Download Circular motion

Circular motion & pendulum
14 May, 2017
know that change of direction is acceleration
know that circular motion is caused by a centripetal
force, and the factors that determine the magnitude of
the force.
Know the meaning of period time, and the effect of length on it.
Outcomes
C: can name the centripetal force, and state which way it acts.
Can explain what periodic time is , and how length alters it.
B: can describe why an object travelling at constant speed in a circle
is accelerating
A: can explain what happens to the size of the force when mass,
speed or radius change.
Plasticene in a horizontal circle
Plasticene in a horizontal circle
• Only relevant force is the pull force of the string trying to
bring the plasticene into the middle. (Can also be called
tension)
The object’s velocity is directed along a
tangent to the circle
Its velocity changes direction as it moves
round
This change of velocity is towards the
centre of the circle.
• The amount of force needed increases
with the speed of the object.
• The amount of force needed increases
with the mass of the object.
• The tighter the circle the more force is
needed.
Pendulum
Pendulum
• It swings because GPE is getting converted into
Kinetic as it falls towards the centre.
• As it travels through the centre GPE is gained again
slowing it down until it stops moving at the
maximum height of the swing.
• It falls towards centre again.
• Friction causes waste energy so it will eventually
stop.
• The periodic time is the time for one swing and
this is constant.
• Changing the mass or amplitude does not alter
the periodic time.
• What else might?
Length of string
• Investigate if it alters periodic time.
•T=1/f
• The periodic time is related to 1/ frequency.
• 24-25 + 32-34
Hydraulics
•Know that pressure in a liquid transmits in all directions.
•Know that pressure is force per unit area
•Know how a hydraulic machine magnifies force.
14 May, 2017
Outcomes
•Explain that liquids transmit force because the molecules are
closely spaced.
•Use P= F/A
•Explain using maths and physics how a hydraulic machine works.
Cartesian diver
Empty and full lemonade
bottle
• Why is it so hard to compress the full bottle?
Empty and full lemonade
bottle
• Why is it so hard to compress the full bottle?
The force is transmitted between the whole fluidthis is because the particles are so close together
and cannot be compressed.
Pressure is the spreading out or
concentration of force.
Drawing pins use this to push into the
material.
P =F/A, all areas in m2, forces in N, pressure
in Pa
Syringes
• The P=F/A is used here
• 30-31
Hydraulic systems
Force = xN
Force = 10N
Y
X
Area =
0.10m2
Piston X puts
pressure on
the liquid
Area =
0.40m2
How do we calculate the pressure that is being applied from piston X?
Hydraulic systems
Force = xN
Force = 10N
f
Y
X
Area =
10cm2
Area =
40cm2
p
pressure
a
= force
area
Hydraulic systems
Force = xN
Force = 10N
Y
X
Area =
0.10m2
The pressure
stays the
same
throughout
the liquid
Area =
0.40m2
What would the pressure be at piston Y?
30-31
Hydraulic systems
Force = xN
Force = 10N
Y
X
Area =
0.10m2
The pressure
stays the
same
throughout
the liquid
Area =
0.40m2
What would the Force on piston Y be?