3.2 Forces in Action Flashcards
Describe what happens when a resultant force F acts on a body with mass m
The body will accelerate in the direction of the resultant force. The resultant force is related to mass and acceleration by the formula f=ma
give 3 ecamples of common forces and explain briefly what they do
weight - the gravitational force acting on an object through its centre of mass
frintion - force that arises when two surfaces rub against each other
drag - resistive force on an object travelling through a fluid (eg water or air)
tension - force within a stretched cable or rope
upthrust - upward buouancy force acting on an object when it is in a fluid
normal contact force - force arising when an object rests against another object. It acts perpendicular to the plane of contact
What is meant by drag
an object moving through a fluid experiences a drag force acting on it. Drag is a frictional force that opposes motion. In air this is air resistance
What is meant by terminal velocity?
when the forces acting on the falling object (eg drag and weight) become balanced so the resultant force is 0. The acceleration becomes 0 and the object is moving at maximum velocity
What is the principle of moments?
For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments
What is a moment?
a turning force: force x perpendicular distance (perpendicular distance from the point to the line of action fo the force)
What is meant by a couple?
A pair of equal and opposite coplanar forces that have equal magnitude and opposite direction, applied to a body parallel to each other but not along the same line.
If you have a uniform object, where would its centre of mass be?
At the geometric centre of the object
Describe what is meant by density
The mass per unit volume of a subsance. The unit is kgm^-3
Describe what is meant by pressure
The pressure is the normal force exerted on a surface per unit area. It is measured in Pascals where 1 Pa = 1Nm^-2
What is the force that an object submerged in a fluid experiences? + Why
It experiences an upwards force called upthrust. This is because the pressure at the bottom surface of the object is greater than at its top surface
State archimedes’ principle
The upthrust exerted on a body immersed in fluid, whether partially or fully submerged, is equal the weight of the fluid that the body displaces. An object will sink if the upthrust is smaller than the weight. For a floating object, its weight is equal to the upthrust/
What can be said about the upthrust acting on a stationary object that is completely submerged in water?
It is equal to the qeight of the object
Which physical quantity has the same base units as energy?
moment
