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# Physics mechanics

### mechanics definitions

What is displacement s of an object? Is the resultant distance moved in a given direction
Define a scalar quantitiy? Has magnitude only
Define a vector quantity? Has magnitude and direction
how can you find the resultant of two vectors? it can be found using a triangle, parallelogram or rectangle to represent them
What are the components of a vector inclined at and angle of ? to the horizontal? horizontal component = V cos ? Vertical component = V sin ?
How do you find the average speed V of an object? Total distance/time
How do you find the instantaneous speed of an object? the rate of change of distance x: V = ^x/^t
What is velocity? the rate of change of displacement S: a = ^s/^t
What is acceleration? the rate of change of velocity V: a = ^v/^t
What does the gradient of a displacement-time graph represent? velocity: v = ^s/^t
What does the gradient of a velocity-time graph represent? acceleration: a = ^v/^t
What does the area under a velocity-time graph represent? displacement
What equation do you use for motion at a constant velocity? v = x/t
What are the equations that are used for motion at constant acceleration? V = u + at S = ut + 1/2at^2 S = 1/2(u+v)t V^2 = u^2 + 2as
How can you describe the horizontal and vertical velocities of a projectile? It moves with constant horizontal velocity and a vertical velocity changing due to acceleration due to free fall
What is the equation that links resultant force on an object to it's mass and acceleration? F = ma
Define the newton. A force that gives a mass of 1 kg an acceleration of 1 m/s^2
What is the equation for weight? Weight = mass x gravitational field strength
Why can't F = ma be used at high speeds? Mass increases with energy
What is viscous drag? Objects moving through air or liquids experience air resistance or viscous drag
What factors does the magnitude of the viscous drag depend on? The medium, the size of the object and the speed of the object
What happens to the viscous drag force when speeds increase? It increases with speed
For an object falling through air explain how an object will reach terminal velocity. For a falling object in air under gravity, the drag increases until it equals the weight. The resultant force and acceleration are then zero so the object continues at a constant.
What is the center of gravity of an object? The point where it's whole weight may be considered to act
Define the moment of a force Force x Perpendicular distance from force line to point
What is a couple? A pair of forces that are equal in magnitude but act in opposite directions, producing rotation.
What is the torque of a couple? One force x perpendicular distance between them
What is the principle of moments? For a body in equilibrium, sum of clockwise moments = sum of anticlockwise moments
What is thinking distance? Distance traveled while the driver reacts Thinking distance = reaction time x speed of vehicle
What is braking distance? Distance traveled after brake has been applied. Depends on mass of vehicle and the efficiency of the brakes, and is proportional to the square of the speed
How do air bags, crumple zones reduce the impact force on a passenger? increase the time and distance taken to come to rest so therefore reduce impact forces
How dopes GPS work? Global Positioning Systems use the transliteration technique
What is work done? Force x Distance moved in direction of the force
Define the joule? The energy transferred when a force of 1N moves a distance of 1m in the direction of the force
What is the conservation of energy? Energy cannot be created or destroyed, only changed from one to another
What is kinetic energy? It is equal to the work done in bringing a moving object to rest. 1/2mv^2
What is gravitational potential energy? mg^h
Define power. The rate of working. work done/time taken
Define a watt. It is developed if 1 joule of energy is transferred in a time of 1 second
Define efficiency. Useful energy output / energy input x 100%
Define density. mass per unit volume. m/V Density of water = 1g/cm^3 = 1000kg/m^3
Define pressure. Force per unit area. F/A Standard atmospheric pressure = 100000N/m^2 = 100kPa
Describe Hooke's law. For a spring or material which is stretched up to it's elastic limit, the extension is proportional to the tension
Define the spring constant. Force per unit extension. F/^x
Describe elastic deformation. Energy is lost and the material is permanently deformed
What does the area under a force-extension graph represent? The work done done in stretching a spring
White down 2 equations for elastic potential energy. 1/2F^x = 1/2k^x^2
Define tensile stress. Force per unit cross-sectional area. F/A
Define tensile strain. Extension per unit length. ^x/L
Define the young modulus. Stress/Strain. Young modulus of steel is 2 x 10^11 Pa
Define ultimate tensile strength. The stress at which a material breaks
Created by: joshsumnerr

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