3.2 Forces In Action Flashcards
What is the centre of mass of an object?
The point at which the weight can be assumed to act.
What does the weight of an object depend on?
It’s mass and the gravitational field strength (W=mg)
What is a free-body diagram?
It is a diagram showing the set of forces acting on a single object
What is weight?
The force due to gravity that acts through an object’s centre of mass
What is friction?
The force that acts between two surfaces in contact to oppose motion
What is drag?
The resistive force that acts on an object moving through a fluid
What is tension?
The force within a stretched object such as a cable or rope
Upthrust
The upward buoyant force that acts on an object in a fluid.
Normal contact force
A force that acts perpendicular to a surface when an object rests on it.
How do you calculate the component of weight down a slope?
W sin (θ) where θ is the angle between the slope and horizontal
How do you calculate the component of weight acting perpendicular to a slope?
W cos (θ) where θ is the angle between the slope and horizontal
What are the key factors in determining the magnitude of drag force acting on an object in a fluid?
Speed and cross-sectional area
Terminal velocity
The maximum speed reached by a falling object when drag and weight are equal.
What is a moment?
The turning effect produced by a force.
Units for moment
Nm
How do you calculate a moment about a point?
Force x perpendicular distance to the line of action of the force
What is meant by a body being in equilibrium?
The net force and the net moment acting on the body are both zero.
What is the principle of moments?
For an object in rotational equilibrium the sum of the clockwise moments about any point is equal to the sum of anticlockwise moments about that point.
What is a couple?
A pair of equal and opposite forces acting on an object with different lines of action.
How do you calculate the moment of a couple?
Force x perpendicular distance between the lines of action of the forces.
What is a triangle of forces?
A vector diagram of the three forces acting on an object in equilibrium
What is a resultant/ net force?
The vector sum of forces acting on an object
What is the density of a substance?
Mass per unit volume
What are the units for density?
kgm^-3
What is pressure?
Normal force acting per unit area
What is Archimedes principle?
The upthrust exerted on a body immersed in fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces.
What is p in the equation p = hρg
Pressure exerted by a fluid
What is ρ in the equation p = hρg
Density of the fluid
What is h in the equation p = hρg
Depth of the fluid
