P5 - Forces and Motion - End of Topic - Part 1
L1 - Scalars and Vectors
A scalar quantity is a quantity with only magnitude; it does not have direction. Examples include: speed, energy, mass, distance.
A vector quantity is a quantity with both direction and magnitude. Examples include: displacement, force, velocity, acceleration.
L2 - Types of Forces
A contact force is a force in which two objects make physical contact with each other in order to exert a force. Examples include friction, air resistance and normal contact.
A non contact force is a force in which two objects do not need to physically touch for a force to be exerted; the force can happen at a distance. Examples include electrostatic, magnetic and gravitational.
L3 - Resultant Forces
When a body experiences a force or several forces, it will have a resultant force in a particular direction given that the forces are not of the same magnitude.
If there is a resultant force of 0N, Newton's First Law states that the object will either remain stationary (if it is already stationary) or continue at the same velocity (if already moving).
If there is a resultant force on an object, it will cause the object to accelerate in a specific direction (direction of force).
L4 - Mass and Weight
Mass is a measure of the amount of matter within an object/number of particles within an object. It is measured in Kg.
Weight is a force and is the result of a mass being present within a gravitational field.
Weight = Mass x Gravitational Field Strength
W = mg
Newtons = Kilograms x Newtons/Kilogram
An object's centre of gravity/mass is the point at which an objects weight acts.
L5 - Work Done
When energy is transferred to a different energy store; work is done.
Work done is the energy transferred when a force causes a displacement of an object.
Work Done = Force x Displacement
W = Fs
Joules = Newtons x Metres
L6 - Hooke's Law
Hooke's Law states that a spring's extension is proportional to the force applied to it.
Hooke's Law shows a relationship of direct proportion up to a limit of proportionality (a point where the spring is deformed in a plastic manner).
Required Practical Method:
- Secure a clamp stand to a surface.
- - Hang the spring you would like to observe on a clamp on the clamp stand.
- - Secure a ruler to the stand, ensure that the "zero" point is aligned with the top of the spring. The ruler should be parallel to the spring.
- - Measure the initial length of the spring.
- - Apply the first force increment, a mass carrier could be used here.
- - Measure the new length of the spring.
- - Subtract the initial value from this to obtain an extension.
- - Continue to add masses and record the extension they cause until the limit of proportionality has been reached.
Independent variable: Force applied to spring
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Dependant variable: Extension of spring/new length
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Control variables: Stiffness of spring, force increments
L7 - Spring Calculations
Elastic Potential Energy = 0.5(Spring Constant(Extension^2))
Ee = 0.5(k(e^2))
Joules = 0.5(Newtons/Metre(Metres^2))
Force = Spring Constant x Extension
F = ke
Newtons = Newtons/Metre x Extension
L8 - Pressure
Pressure = Force / Area
p = F / A
Pascals = Newtons / Metres^2
L9 - Pressure in a Fluid
Pressure = Density x Gravitational Field Strength x Height
p = ρgh
Pascals = Kilograms/Meter^3 x N/kg x Metres
Density of water = 997kg/m^3
Pascals vases - Water levels remain constant in a container, no matter the shape of each section of the container; this is because pressure must be equal at all points in the fluid. Pressure is unaffected by area, density is constant and pressure is constant so the depth will be equal throughout.
L10 - Upthrust
Archimedes principle states that when an object is completely or partially submerged, the upthrust acting on it is a force equal to the weight of water that the object displaces.
Upthrust = Density x Volume x Gravitation Field Strength
U = ρVg
Newtons = kg/m^3 x Metres^3 x Newtons/Metre
L13 - Speed
Speed = Distance / Time
v = s / t
Metres/Second = Metres / Seconds
L14 - Distance Time Graphs
Walking - 1.5m/s
Running - 3.0m/s
Cycling - 6.0m/s
Sound - 330.0m/s
The gradient on a distance time graph is representative of the speed.
L15 - Velocity Time Graphs
The gradient of a velocity time graph is representative of the acceleration; a negative gradient implies that a deceleration is taking place.
The total area under a velocity time graph is the total distance travelled.