physics 1.2 kinematics or mechanics

7/30/2019 Physics 1.2 kinematics or mechanics

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Unit 1 Topic 2.1

Materials

Fluid Flow

Factors that affect fluid flow:- Pressure- Heat- Gradient- Surface texture- Shape of pipe- Viscosity

Fluids

- Any substance that can flowDensity

- The measure of mass per unit volumeDensity = mass/volume

Up thrustthe upward force on an object submerged in the fluid caused by pressure

Archimedes Principle: the size of the force is equal to the weight of the fluid that has

been displaced by the object

Note: when an object is completely submerged, the mass of the fluid displaced is

equal to the volume of the object multiplied by the density of the fluid

Weight of fluid displaced:

W = mg

Floating

Note: when an object is at the surface there is no up thrust because there is no fluid

being displaced

- When the object sinks, the deeper it sinks the greater the volume of fluid itdisplaces therefore increasing the up thrust force acting on it

- If up thrust and weight are balanced, the object floatsNote: so for the object to float it would have to sink until it displaces its own weight

in the fluid

The Hydrometer floating at different depths

Note: instrument used to determine the density of the fluid

- Hydrometers have a constant weightIn less dense fluids


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- The hydrometer will sink more because it must displace more fluid tobalance out its weight

Note: there are scale markings on the side of a hydrometer that indicate the density

of the fluid

Fluid MovementSmaller area to air resistance = reduced opposing/slowing down force

Laminar/Streamline Flow: occurs at lower speeds, smooth flow where pressure is

even everywhere, always at steady speeds in the same direction (constant velocity)

Turbulent Flow: as speed increases, the behavior of the object flowing becomes

unpredictable and velocity constantly changes and pressure increases, eddy

currents are also made which increases drag force (if it was cars it would also

increase fuel consumption

Newtonian liquids: liquids that follow Isaac newtons formulae

Drag Act

Viscous drag: the friction force in fluids

Viscous: the thickness of the fluid

Note: if the frictional force caused by the movement through a fluid is small we say

that viscosity is low

Coefficient of viscosity: Greek letter eta, n

Rate of flow of a fluid moving through a pipe is inversely proportional to viscosity

Factors that affect viscosity:

- Temperature: increasing temperature decreases viscosityNote: for gases, viscosity increases with temperature

Terminal Velocity

Acceleration due to gravity near the surface of the earth = 9.81ms-2

Newtons second law: a = sum of Fxm

- Take account and sum up all the forces acting on the object falling through afluid, we can find the resultant force and therefore find the resulting

acceleration

Forces we take into account:

- Weight- Up thrust- Viscous drag


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Viscous Drag

- The friction force between a solid and a fluidTerminal velocity is proportional to the square of the radius

- The larger the sphere the faster it falls

physics 1.2 kinematics or mechanics

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