Chapter 4, Forces Flashcards
Defining equation for force?
F=ma (force=mass*acceleration).
Unit for force?
Newtons.
Difference between mass and weight?
Mass (measured in kg) is how much stuff there is, weight (measured in N) is the product of mass and g and gives the force applied to an object towards the centre of mass of the object it is in the gravitational field of.
What is the centre of mass?
The point in an object through which weight acts, also if a force is applied through the centre of mass there is no net moment.
How do you find the centre of mass of an object?
if you hang an object from a point you know the line through the point which is perpendicular to the earth goes through the centre of mass. You can use a plumb-line to help measure this position.
What is weight?
The gravitational force acting through the centre of mass of an object.
What is friction?
The resistive force from two rough objects rubbing against each other.
What is drag?
The resistive force acting on an object travelling through a fluid.
What is tension?
The force within a stretched object (usually string/rope)
What is upthrust?
An upwards force acting on an object inside a fluid caused by the displacement of this fluid.
What is the normal contact force?
The force acting 90 degrees to the surface an object is resting on stopping it falling through the object.
On a smooth slope with an object resting on it what is the value of the normal contact force and the component of the weight down the slope?
Normal contact = component of weight perpendicular to slope = mgcos(theta), component of weight down slope = mgsin(theta).
What are the main factors that is drag proportional to?
Speed of the object and cross sectional area, also shape of object, roughness/texture of object and the density and viscosity of the fluid.
What is terminal velocity?
The point of equilibrium between weight and the drag force such that the net force is 0.
What is the equation for the moment of a force?
moment = force * perpendicular distance.
Unit for moments?
Newton meters.
What is the principle of moments?
For a body in rotational equilibrium the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about that same point.
What is a couple?
Two equal forces acting in opposite directions about a point such that it rotates without having any displacement.
What is the defining equation for density?
ρ = m/V (density = mass/volume).
What is the defining equation for pressure?
p = F/A (pressure = force/area).
What is the unit for pressure?
The Pascal (Pa).
What does the equation p=hρg show?
pressure = height fluid column * density of liquid * acceleration due to gravity.
What is the equation for upthrust?
upthrust = Axρg where A is the area on top, x is the height of the submerged object, ρ is pressure and g is acceleration due to gravity.
What is Archimedes principle?
The upthrust exerted on a body in a fluid is equal to the weight of the fluid that body displaces.
