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Name ______________________
Teacher _______________________
Forces and Gas
CfE Physics Level 4
Forces S3 course content
Physics Skill
Numeracy Skill
Literacy Skill
SPEED
I can use appropriate methods to measure, calculate and display graphically the speed
of an object, and show how these methods can be used in a selected application. SCN
4-07a
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I can use “movie maker” or similar software to measure the average speed of an object.
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I can use a timer and trundle wheel to measure the average speed of a car.
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I can use “movie maker” or similar software to measure the instantaneous speed of an
object.
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I can use a laptop and light gate to measure the instantaneous speed of a trolley on a slope.
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I can answer numerical questions on speed (v=d/t) using the correct layout.
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I can rearrange a simple three term equation. (d=vt)
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I can convert units of speed from m/s into km/s and km/hr and vice versa.
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I can design and write up a simple scientific experiment to measure the speed of a trolley
down a slope, in the appropriate format.
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I can identify the motion of an object from its speed time graph, using the terms “accelerate”,
“constant speed” and “decelerate” correctly.
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I can sketch the speed of an object using excel spreadsheets and chart wizard.
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I can draw a good quality line graph on graph paper.
ACCELERATION AND FORCE
By making accurate measurements of speed and acceleration, I can relate the motion of
an object to the force acting on it and apply this knowledge to transport safety. SCN 407b

I can state Newton’s First Law and use it to describe the motion of objects in a car crash
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I can calculate the acceleration of an object by measuring its initial and final velocity and the
time it takes between them.
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I can use the PASCO equipment with Science Workshop or the light gates with data logger to
measure the acceleration of a trolley on a slope.
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I can design an experiment which will allow me to measure the acceleration of a golf ball
falling through the air.
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I can state the unit for Force and can describe how to measure the Force required to move
different objects.
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I can state Newton’s Second Law in terms of Force, Mass and Acceleration
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I have used and can describe an experiment which will show that a large force provides a
large acceleration
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I can use the Equation F=ma in context and rearrange its term appropriately.
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I can use the terms “deceleration” and “average force” to describe some of the safety
features in modern car design; namely crumple zones, seatbelts and airbags.
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I have used the pimp my trolley equipment to minimise the damage to a trolley
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I have investigated some of the techniques used by spacecraft to slow their decent onto a
planet.
FLOATING AND SINKING
Through experimentation, I can explain floating and sinking in terms of the relative
densities of different materials. SCN 4-08b

I have created a model which shows the relative densities of liquids
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I can use and rearrange the equation þ = m/v in context and can explain each term and its
units
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I can state that less dense materials will float on top of materials with greater density
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I can increase the volume of an object so that its density will change and it will float.
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I can decrease the mass of an object so that its density will change and it will float.
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I have investigated a historical event involving lighter than air balloons.
IDEAL GAS
I have developed my understanding of the kinetic model of gas. I can describe the
qualitative relationships between pressure, volume and temperature of a gas. SCN 405a

I can sketch the particle arrangement in a solid liquid and gas
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I can describe the kinetic model of a gas
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I know the phrase “absolute zero” and what it means in terms of particle movement
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I can use the Kinetic model to explain a simple demonstration involving a gas
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I can describe the relationship between Pressure, Volume and Temperature in terms of
movement of particles.
Section 1 Forces and Motion
The speed of an object is obtained by using the formula:
In order to measure the speed of an
object, the distance travelled (in metres) and the time taken (in seconds) must be measured. We did this
in various ways;
Average speed (the speed over the whole journey)
Film a car over a set distance and use the software to note the time
Use a ruler / trundle wheel and stopwatch
Instantaneous speed (the speed during a very short time interval)
Film a car passing a point and take a note of the time taken and the length of the car
Use a piece of card of known length and light gate attached to a computer
The acceleration of an object can be calculated using the formula:
In order to measure the acceleration of an object two instantaneous speeds are needed, as well as the
amount of time between them (eg cars are quoted as 0 – 60 mph in 6.5 seconds).
Forces
The force applied to an object will determine its motion. However an object’s mass must also be taken
into account. This can be neatly summed up by using Isaac Newton’s first two laws of motion.
Newton’s 1st law – when an object is acted upon by a balanced (or zero overall) force then the object
will stay at rest, or continue at the same speed (constant) in a straight line.
Seatbelts are designed to supply a safe stopping force to a person when their car
suddenly comes to a stop, otherwise the person would keep moving until they hit something!
Balanced forces ====== constant (same) motion
Newton’s 2nd law – when an object is acted upon by an unbalanced force then the object will change
its motion (accelerate/decelerate and/or change direction). If it is a large mass object it will not change
its motion much, if it is a small mass it will change by a large amount.
A formula one racing car is made to be as powerful (large force) as possible but still be a
light (small mass) as possible. This combination will allow it the greatest acceleration.
Unbalanced forces === Change (accelerate) motion
Unbalanced Force = mass x acceleration
F = ma
Section 2 Solids, Liquids and Gases
All material we see and touch is made from tiny particles called atoms (or molecules in a compound).
These can be close together and fixed in position (solid). Close together and not fixed in position
(liquid). Far apart and free to move (gas).
The density of a material is a measure of how much mass (number of particles) is squeezed into a
particular volume. A small, high mass material has a high density whereas a large, low mass material
has a low density.
Density can be calculated in the following way:
Solid; Measure mass directly on a balance. Use V = l x b x h or “Archimedes principal” to measure
volume.
Liquid; Measure mass of container, add the liquid and measure new mass.
Mass of liquid = mass of both – mass of container.
Measure volume using measuring cylinder
Gas; Measure mass of gas and container. Remove gas with a vacuum pump, measure new mass. Mass
of gas = mass of both – mass of container.
Replace space in empty container with water, measure volume of water using a measuring
cylinder.
An object will float if it is less dense than the liquid it is placed in. Oil will float in water, but treacle
will sink in water. A large, massive ship can be made to float if its volume is so large that its overall
density is less than that of water (1000kgm-3). A balloon can be made to float in air if its overall density
is less than the surrounding air (about 1.2 kgm-3).
Gas Laws
The kinetic theory of gases can explain how temperature (T), volume (V) and pressure (P) are related.
It states that a gas is made of tiny particles that are free to move, bump off each other and the walls.
T vs P with fixed Volume: A gas at a higher temperature has more energy, so the particles have more
energy and therefore move more quickly. They bump off the walls more often and with more force,
increasing the pressure.
(T up ---- V up)
T vs V with fixed Pressure: A gas at a higher temperature has more energy, so the particles have more
energy and therefore move more quickly. They bump off the walls more often and with more force,
pushing the walls apart and increasing the volume of the container.
(T up ---- V up)
V vs P with fixed Temperature: A gas which has less space for the particles to move around means that
the particle hit the walls more often. The overall force on the wall increases as does the pressure.
Note, the particles don’t move any faster as their temperature is the same. (V up ---- P down)
You should be able to use the kinetic theory to explain some of the demonstrations you experienced in
this topic.