P11.1 Pressure and surfaces AQA GCSE Physics Force And Pressure Kerboodle Answers: Page No. 163
1 a When you do a handstand, the pressure on your hands is greater than the pressure on your feet when you stand upright because the contact area on the hands is smaller than the area on the feet.Since the weight exerted is the same, the pressure exerted on your hands when you do a handstand is greater as pressure = force / area. b Snowshoes like the one shown in Figure 3 are useful for walking across soft snow, The reason is that the contact area of the snowshoes on the ground is much bigger than it would be with normal shoes. So the snowshoes reduce the pressure on the ground because its weight is spread over a much bigger contact area. 2 a laid flat on a bed of sand Pressure = force/area = 1200/0.60*0.40 =800Pa b standing upright on its short side Pressure = force/area = 1200/0.40*0.05 = 150Pa 3 A pressure vessel is fitted with a valve that opens if the difference in the pressure in the vessel and the outside pressure is greater than 45 kPa. The valve contains a spring that exerts a force on a disc in the valve to keep the valve closed. The pressure acts on a disc area of 0.0002m2. the force needed to open the valve Pressure=force/area So force = 45000*0.0002=9N 3 The four tyres of a car of weight 9400 N are inflated to a pressure of 180 kPa. the contact area of each tyre on the ground Pressure=force/area, So area = force/pressure = 9400/180000= 0.0522 metre square.Then area on each tyre=0.0522/4=0.01305metre squareP11.2 Pressure in a liquid at rest AQA GCSE Physics Force And Pressure Kerboodle Answers: Page No. 165
1 a the wall of a dam needs to be thicker at the base than at the top because the pressure of the water is much greater deeper down and the dam needs to be thick at the bottom so that it is strong enough to withstand this larger pressure. b A water tank at the top of a tall building supplies water to taps in the building, the pressure of the water from a tap on the ground floor is greater than the pressure from a tap on a higher floor because pressure = hpg so pressure is directly proportional to height of water column and water tank is in more height from ground floor. 2 A rainwater gutter collects rainwater that runs off a sloped roof.The water in the gutter runs into a vertical downpipe joined to one end of the gutter. the downpipe end of the gutter needs to be no higher than the other end because pressure = hpg so pressure is directly proportional to height of water column so to increase pressure the downpipe end of the gutter needs to be no higher than the other end. 3 A sink plug has an area of 0.0006m2. It is used to block the outlet of a sink filled with water to a depth of 0.090m. a the pressure on the plug due to the water , pressure = pgh = 1000*9.8*0.090 = 822Pa b the force needed to remove the plug from the outlet, force = pressure*area = 822*0.0006 = 0.4932N 4 Now in figure 3 tap water level is higher than sea water level because density of sea water is 1.025kg/L and tap water is 1kg/L so taop water is less denser than sea water.so greater depth of tap water is needed to create same pressure.P11.3 Atmospheric pressure AQA GCSE Physics Force And Pressure Kerboodle Answers: Page No. 167
1 atmospheric pressure acts when you drink through a straw, A drinking straw only works when the air in the straw is sucked out.Without any air in the straw, atmospheric pressure acting on the liquid surface outside the straw pushes liquid up the straw. 2 atmospheric pressure decreases with height above sea level because the density of the atmosphere decreases with increasing height above the ground (i.e., increasing altitude). This is because the weight of air pressing down on a horizontal surface at any altitude decreases with altitude. So there are fewer molecules per cubic metre and therefore fewer impacts per second at a higher altitude. So atmospheric pressure decreases with increasing altitude. . In effect, the weight of air above any given altitude exerts pressure on the air below. At increased altitude, there is less weight of air above, so atmospheric pressure decreases with increasing altitude. 3 A suction cap on a wall tile has a surface area of 1.2 x 10-3m2 in contact with the tile. The force needed to pull the suction cap off the tile = pressure*area = 100000*0.0012 = 120NP11.4 Up thrust and flotation AQA GCSE Physics Force And Pressure Kerboodle Answers: Page No. 169
1 a it is difficult to hold an inflated plastic ball underwater Because water is much more dense than air. Less dense always goes up. Same thing goes for the cork. It is less dense than water, so it floats. Well, an inflated plastic ball is difficult to hold underwater because the air inside of the ball is buoyant, and so it wants to float on the water, and not be trapped underneath. b cork is a suitable material for filling a life belt because cork, balsa wood and kapok (a naturally buoyant material from a tropical tree that’s also used in mattresses and insulation) have been used in inherently buoyant life jackets. 2 a the reading on the newton-meter is less when the object is in water because when the object is in the water, it experiences an upthrust The difference between the two newton-meter readings is equal to the upthrust on the object. b the newton-meter reading changes as the object is lowered into water because the newton-meter reading is less when the object is in water. This is because when the metal object is in the water, it experiences an upthrustThe difference between the two newton-meter readings is equal to the upthrust on the object. Repeat the test with the same object only partly immersed in the water. You should find that the newton-meter reading is in between the two earlier readings. This is because the upthrust is less when the object Is only partly Immersed in the water. 3 a Ice floats on water because ice is less dense than water so it floats on water. b i object has the greatest density because the Block A has greatest density because it sinks in a bowl of water. Sinks because its weight is greater than the weight of the liquid displaced. So the weight of the object is greater than the upthrust on the object when it is fully immersed. ii Block B has lowest density because an object that is less dense than the liquid floats because its weight is less than the weight of the liquid it displaces. So the weight of the object is less than the upthrust on the object when it is fully immersed. 4 a Using the equation pressure=hpg, it can be shown that the upthrust is equal to the weight of liquid displaced.so lengh of tube above water depends on the total weight of the tube.Summary questions AQA GCSE Physics Force And Pressure:Kerboodle Answer Page No. 170
1 a The sink plug is 8.5 cm below the water surface. The pressure due to the water on the sink plug = 0.085 m × 1000 kg/m3 × 10 N/kg= 850 Pa b The sink plug has an area of 6.0x 10^m2, the force needed to remove the sink plug= 850 Pa × 6.0 × 10−4 m2 = 0.51 Newton 2 a The blood pressure of a healthy person is 120 mm of mercury. This pressure in pascals = 0.120 m × 13 600 kg/m3 × 10 N/kg = 16 320 Pa = 16.3 Pascal b The precision of the reading of a mercury gauge is 2 mm. the gauge is more precise than an electronic gauge that gives readings with an accuracy of 50 Pa, p = 0.122 m × 13 600 kg/m3 × 10 N/kg = 16 590 Pa = 16.6 kPa; precision of mercury gauge = 0.3 kPa or 300 kPa 3 a The overall height of this model atmosphere would be no more than 7800m. p = 7800 m × 1.3 kg/m3 × 10 N/kg = 1.01 × 105 Pa = 101 kPa = atmospheric pressure at sea level, so overall height = 7800 m B As 7800 m gives precise value of atm pressure and it is not feasible to assume the density constant. As we know that density of atmosphere above sea level is less than density at sea level 4 a the barge is acted on by an upthrust because the pressure of water directly below the barge is greater than atmospheric pressure, upthrust on barge because force of water pressure on bottom is greater than force because of the atmospheric pressure on top b i the pressure of the water on the hull is 2.5 m × 1000 kg/m3 × 10 N/kg = 25 kPa ii The barge has a flat hull of area 80m2. the upthrust on the barge is 25 000 Pa × 80 m 2 = 2000 kN c When the barge is unloaded, it floats higher in the water than when it is loaded because the upthrust on loaded barge is equal to the whole weight of barge in addition with load, but when boat is unloaded, upthrust makes to push the barge up and as a result of it if the barge rises, upthrust decreases because barge displaces less water as it rises, barge stops rising when upthrust is equal to unloaded weight of barge 5 The prognosis: density increases as the amount of dissolved salts increases as dissolved salt adds more particles per cubic meter / objects float more easily in salt water than ordinary water or salt water density decreases because extra particles increase the volume of the solution more than the mass, The experiment: measure the salt dough using the mass balance, add the measured salt dough to the water and dissolve it, replace the test tube in the solution and measure the length again, repeat several times, adding each time the measured salt dough to the solution and dissolution of the added salt before measuring the length, record the aggregate mass, the total mass of dissolved salt and the length in the table, use aggregate mass measurements to calculate the total salt mass for each measured length, 6 a i the pressure due to the sea water on the craft at this depth is calculated as follows: p = hρg p = 250 m ×1100 kg/m3 × 9.8 N/kg p = 2 695 000 Pa = 2.7 × 106 Pa II the force on the window due to the pressure difference between the inside and outside of the window is calculated as follows; Outside Pressure = 2 695 000 Pa + 100 000 Pa = 2 795 000 Pa Inside Pressure= 100kPa = 100 000 Pa Force on window = Pressure difference × area = (2795 000 Pa – 100 000 Pa) × 0.043 m3 = 115885 NewtonPractice questions AQA GCSE Physics Force And Pressure: Kerboodle Answer Page No. 171
01.1 the most suitable design and give a reason for your choice is C Because the pressure of water increases with depth, walls must be thicker near the bottom 01.2 three lines drawn – one from each spout. Distance from can should increase with depth 01.3 it important to keep the can filled with water in the investigation because to maintain the pressure of water in the can to compare results 01.4 New scuba divers are only allowed to dive to a depth of about 18 m. the water pressure at a depth of 18m is 18 0810 Pa 02.1 it is important for the hand cart to have wide wheels because pressure = force ÷ area, so the bigger the area of the wheels, the less pressure on the sand and it won’t sink in 02.2 The mass of the handcart and equipment is 85 kg. Each wheel has an area of 0.015m’1 in contact with the sand. pressure of the handcart and equipment on the wet sand is 27 800 N/m2 03.1 dry the inside of the pycnometer using acetone or similar,weigh the pycnometer, fill with the oil to the correct volume mark, ensure the temperature of the oil is correct, weigh the pycnometer and oil, calculate density using,density = weight ÷ volume wash out pycnometer and dry between samples of oil take care using glassware by wearing gloves 03.2 correct labels from top: methanol; castor oil; sea water; glycerol 03.3 A plimsoll line is drawn on merchant ships to show the ship Is not overloaded with cargo. As the ship is loaded it will sink lower and lower into water. So it will displace more and more water and the upthrust increases. The ship will float when its weight is equal to the upthrust. 04.1 Passenger airlines fly at about 12000m. At this height the cabin ispressurised to a pressure equal to the atmospheric pressure at 2000 m. the cabin pressure is 80 kPa 04.2 A design goal for many newer aircraft is to lower the cabin altitude, which can be beneficial for passenger comfort. The reason is that the higher the cabin pressure the closer it gets to the air pressure on landing and taking off passengers’ don’t suffer effects of altitude such as ears ‘popping’ and other effects 04.3 A passenger drank from a plastic bottle of water whilst flying in the aircraft, He screwed the top back on and returned the bottle to his rucksack when the bottle was empty. The passenger found the plastic bottle had crushed on landing as whilst flying the air in the bottle is at lower pressure so there are fewer air molecules. On landing the air pressure is greater outside the bottle than inside. Therefore the bottle crushes inwards.Disclaimer
Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it. References: BBC Bitesize AQA GCSE Science Kerboodle textbook Wikipedia Wikimedia Commons Join Our Free Facebook Group : Get A* in GCSE and A LEVEL Science and Maths by Mahima Laroyia: https://www.facebook.com/groups/expertguidance.co.uk/ For Free Tips, advice and Maths and Science HelpThis page contains the detailed and easy notes for AQA GCSE Physics Forces for revision and understanding Forces.
AQA GCSE Paper 1: Complete Revision Summary
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FORCES
4.5 FORCES
- Scalar and vector Quantites
- Contact and non – contact Forces
- Gravity
- Resultant Forces
- Work Done and Energy transfer
- Forces and Elasticity
- Moments, Levers and Gears
- Pressure in a Fluid
- Atmospheric pressure
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FORCES AND MOTION
Distance and Displacement Speed, Velocity, Acceleration Distance Time Graph Velocity Time Graph
NEWTONS LAW OF MOTION
Newtons First Law
Newtons Second Law
Newtons Third Law
Forces and Breaking
Breaking Distance
Thinking Distance
Reaction Time
MOMENTUM
Momentum
Conservation of Momentum
SCALARS AND VECTORS
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DISTANCE AND DISPLACEMENT
- Distance is scalar Quantity
- Displacement is a vector Quantity
- Displacement is speed in a given
direction
CONTACT AND NON CONTACT FORCES
Force is push or pull on an object that causes an object due to
interaction with another object that causes an object to:-
a) change speed
b) Change direction
c) change shape
FRICTION FORCE
It is a necessary evil
Friction is a contact force that opposed motion between the
two surfaces that are in physical contact.
- It is a resistive force
- It happens in the opposite direction of motion.
a) It helps to light a matchstick.
b) The friction between the tyres and the
roads prevent the vehicle to slide.
a) It can cause wear and tear of machines
b) It can cause wear and tear of tyres
NEWTONS THIRD LAW OF MOTION
THE SKATERS MOVE TOWARDS EACH OTHER
AS THEY PULL ON EACH OTHER WITH EQUAL
AND OPPOSITE FORCE
RESULTANT FORCES
Net force = 0 N ( forces are balanced)
The body will stay at rest
It is the total force that acts on the body. It is the sum
of all the forces that acts on the body .
The resultant force decides the speed and the direction
of the body.
BALANCED
If the resultant force is zero
- If the forces are balanced and
the body is at rest then it will
stay at rest. - If the forces are balanced and the
body is moving it will keep on moving
with the same speed and direction
UNBALANCED
If the resultant force is
non zero
The body will
move in the direction
of resultant force.
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NEWTONS FIRST LAW OF MOTION
If an object is at rest it will remain at rest
If an object is in motion it will continue to move with the same
speed and direction unless no resultant force acts on it.
If the resultant force is non zero or unbalance the object will
move or change speed or direction.
MOMENTS
It is the turning effect of force.
MOMENT =. Force. X Perpendicular distance
from the pivot
Nm = Nxm
Greater distance from the pivot increases
the moment or the turning effort
so a small effor can lift a heavy load.
MOMENT QUESTIONS
Moment = Force X distance
= 30 X 10
= 300 Nm
Q2 The moment of a spanner is 50 Nm.
Calculate the force acting at a distance of
10m from the pivot.
LEVERS AND GEARS
Simple Lever and Force Multipliers
In all these levers, the turning effect of force is greater by increasing the distance of effort
further away from the pivot. It increases the turning effect and multiply the force with a
small effort.
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GEARS
GEARS TRANSMIT TURNING EFFECT OF
FORCE
- Gear A Connected to the engine
- Smaller radius
GearB
- Bigger radius
- Connected to Wheels
At the Point of Contact they exert equal and opposite force.
Turning effect is greater due to greater radius .
Low gear
- Low speed and high turning
effect - small gear wheel run a bigger
gear wheel - bigger wheel has greater turning
effect but slow speed
High Gear
- High speed and
low turning effect - large gear wheel run
a smaller gear wheel - small gear wheel force
acts near to the shaft it
run faster with a high speed
but lower turning effect
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MOMENTS AND EQUILBRIUM
The sum of clockwise moments=
The sum of anticlockwise moments
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WEIGHT OF THE BEAM
CENTRE OF MASS
It is the point at which the entire mass of the object
can be thought as being concentrated.
CENTRE OF MASS FOR SYMMETRIC OBJECTS
- It is along the point of symmetry
- If there more line of symmetry the centre of mass
is at the intersection of lines of symmetry
SUSPENDED OBJECT
- The center of mass is directly below the point of suspension.
- When suspended, the weight will give the turning effect and
it will come back to its equilbrium position
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SPEED, VELOCITY AND ACCELERATION
Q1 A car is travelling at the speed of 20 m/s.
Calculate the distance covered in 10 minutes
DISTANCE TIME GRAPHS
VELOCITY TIME GRAPHS
SLOPE OF VELOCITY TIME GRAPH= ACCELERATION
AREA UNDER THE GRAPH = DISTANCE
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EQUATIONS OF MOTION
NEWTONS SECOND LAW OF MOTION
The acceleration of a body is
a) directly proportional to the resultant force
b) inversely proportional to the mass of an object
NEWTONS SECOND LAW OF MOTION
F = Mass x acceleration
SPEED UP
- The velocity of the object increases.
- The object accelerated.
- The resultant force is in the direction of motion.
SPEED DOWN
- The velocity of the object decreases .
- The object is decelerated.
- The resultant force is opposite to the direction of motion.
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WEIGHT AND TERMINAL VELOCITY
Weight (N) = Mass (Kg) x GRAVITATIONAL FIELD
STRENGTH (N/Kg)
g on earth = 9.8 N/Kg
or 10 N/Kg
FORCE AND WORK RELATIONSHIP
Q1 Calculate the work done when the force of 100 N moves the object
to a distance of 2m ?
W =F x S
= 100 x 2
= 200J
Q2 Calculate the force applied when 100 J of work is done to move
an object to a distance of 5 m ?
TERMINAL VELOCITY
It is the constant velocity of an object when
the resultant force is zero and the weight
of the body is balanced by the drag and
body has zero acceleration.
Terminal Velocity
TERMINAL VELOCITY IN FLUIDS
- In fluids, weight of the object is balanced by frictional force acting
upwards. - The body falls with constant velocity as net force or resultant force
acting on the object is zero, so the body falls at constant velocity
called the terminal velocity.
FORCES AND BREAKING
STOPPING DISTANCE
- The shortest distance a vehicle
can safely stop in. - It is the sum of thinking distance
and braking distance.
THINKING DISTANCE
The distance travelled by the body
during its reaction time.
= Speed x reaction time
Affected by tiredness, drug, alcohols
as all these affects the reaction time.
BRAKING DISTANCE
- Distance travelled by the body when
the braking force is applied. - Poor weather conditions, road conditions,
poorly maintained vehicles, speed of
the vehicle and the mass of the vehicle
affects the same.
MOMENTUM
Principle of conservation of momentum
- Momentum is a vector quantity .
- It has a magnitude as well as direction.
- Greater the speed, greater the momentum.
- Higher the velocity, higher the momentum.
CONSERVATION OF MOMENTUM
IMPACT FORCES
Relationship between force and momentum
If we increase the time and the momentum is conserved,
the impact force can be decreased.
So greater impact time = reduced impact force
CAR SAFETY FEATURES
All these features increases the impact time, decreasing the momentum and thus
reduced the impact force.
FORCES AND ELASTICITY
Effect of force on elastic objects:-
Change shape or deformation by
- Bending
- Stretching
- Compressing
Elastic Deformation
Object regains its original shape when
the force is removed like stretched rubber
band.
Inelastic Deformation
Object that does not gain its original shape
and changes shape permanently.
Example: overly stretched rubber.
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FORCES AND ELASTICITY
HOOKE’s LAW
Force on a spring is directly proportional
to the extension until it reaches its
limit of proportionality.
FORCES AND ELASTICITY
SPRING CONTSTANT
It is the measure of the stiffness of the spring.
Greater the spring constant stiffer is the object.
LIMIT OF PROPORTIONALITY
It is the point upto which the springs obeys
Hooke’s law. Beyond this point, the object
comes in the plastic region and no longer
obeys the Hooke’s law.
Q1 Calculate the force applied on the spring when
it is extended by 2m. The spring constant is 5N/m
F = k e
=5 x 2
=10 N
Q2 Calculate the spring constant of a spring when a force
of 50N extends the spring by 5 m.
K F/e
=50/2
=10 N/m
ELASTIC POTENTIAL ENERGY
E =1/2 k e 2
E = Elastic potential energy (J)
K = spring constant (N/m)
e= extention in the spring (m)
Elastic potential energy is the
energy stored in the spring when
it is stretched or compressed.
PRESSURE
- Greater the force greater the pressure .
- Smaller the area more will be the pressure exerted.
PRESSURE IN LIQUIDS
ATMOSPHERIC PRESSURE
- Atmospheric pressure arises due to
collission of the airparticles with the
Earth’s surface. - It decreases with altitude as the number
of particles decreases with height
causing decrease in weight.
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KEY TERMS
a) Forces :-Force is push or pull on an object that causes an
object due to
interaction with another object that causes an
object to:-
a) change speed
b) Change direction
c) change shape
b) Scalar :-Quantity that has magnitude only.
eg Length, Area, Volume etc .
c) Vector : Quantity that has magnitude
as well as direction. eg Displacement,
velocity, acceleration, momentum.
d) Friction :Friction is a contact force that opposed motion
between the
two surfaces that are in physical contact.
e) Newton First Law of Motion :-If an object is at rest it will remain at rest
If an object is in motion it will continue to
move with the same
speed and direction unless no resultant force
acts on it.
f) Newton Second Law of Motion:- The acceleration of a body is
a) directly proportional to the resultant force
b) inversely proportional to the mass of an object.
g) Newton Third Law of Motion:-For an every action force, there is an
equal and opposite reaction force.
h) Resultant Force It is the total force that
acts on the body. It is the sum
of all the forces that acts on the body .The
resultant force decides the speed and the
direction
of the body.
i) Free Body digrams are the graphical
illustration to represent all the forces
acting on a body.
j) Moments: It is the turning effect of force. It
is calculated by force multiplied by the
perpendicular distance from the pivot.
k) Levers : In all these levers, the turning
effect of force is greater by increasing the
distance of effort
further away from the pivot. It increases the
turning effect and multiply the force with a
small effort.
l) Gears : GEARS TRANSMIT TURNING EFFECT OF
FORCE.
m)Centre of Mass: It is the point at which the
entire mass of the object
can be thought as being concentrated.
n) Speed: It is the distance travelled divided by
the time taken.
o) Velocity: Speed in a given direction.
p) Acceleration: It is the change in speed over
time taken.
q)Weight: It is the force acting on the body due to gravity.
r) Terminal Velocity: It is the constant velocity
of an object when
the resultant force is zero and the weight
of the body is balanced by the drag and
body has zero acceleration.
s) Thinking Distance: The distance travelled by
the body during its reaction time.
t) Breaking Distance: Distance travelled by the
body when the braking force is applied.
u)Momentum: It is the product of mass and
velocity.
v) Conservation of Momentum: In a closed system,
the momentum before
the collission and after the collission remains
unchanged.
w) Hooke’s Law: Force on a spring is directly
proportional
to the extension until it reaches its
limit of proportionality.
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Disclaimer:
I have tried my level best to cover the maximum of your specification. But this is not the alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.
References:
BBC Bitesize
Wikipedia
Wikimedia Commons
Image Source:
Wikipedia
Wikimedia
Commons
Flickr
Pixabay
Make sure you have watched the above videos and are familiar with the key definations before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well.
P11-Force And Pressure
Disclaimer
Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.
References:
BBC Bitesize
AQA GCSE Science Kerboodle textbook
Wikipedia
Wikimedia Commons
Join Our Free Facebook Group : Get A* in GCSE and A LEVEL Science and Maths by Mahima Laroyia: https://www.facebook.com/groups/expertguidance.co.uk/
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