Forces in action Flashcards
What is net resultant force
A net resultant force causes an object to accelerate in the direction of the force.
What is a newton
A newton is the measurement of force, defined as the force that gives an object of 1kg mass an acceleration of 1ms^-2
What is the difference between mass and weight
Mass is an intrinsic scalar property of an object representing the amount of matter it contains, while weight is the force exerted on that mass due to gravity, making it variable depending on the gravitational context.
What is a centre of mass
An imaginary point of an object where the weight of the object appears to act. Any external force applied on the centre of mass will cause a straight line of motion.
How do you use a plumb line to find the centre of gravity of a card
Make small holes along the edges of the object made from card. Insert a pin through one of the holes and hold the pin firmly in a clamp. Allow the object to swing freely. It will come to rest with its centre of gravity vertically below the pin. Hang a plumb-line from the pin and draw a line along the vertical string of the plumb-line. Repeat this process for other holes. The centre of gravity will be the point of intersection of the lines.
What is friction
The force that arises when 2 surface rub against each other
What is drag
The resistive force on an object travelling through a fluid. Changes based on the speed, cross sectional area of object and the density of fluid. Directly proportional to velocity squared.
What is tension
The force within a stretched rope
What is upthrust
The upward buoyancy force acting on an object when it is in a fluid.
What is normal contact force
The force that arises when an object rests against another object.
What is terminal velocity
The maximum constant speed a free falling object reaches when its net resultant force is 0. When drag is equal to weight, acceleration is 0 and terminal velocity is reached.
What is a moment
The turning effect of a force about some axis or point.
How to calculate moments
Force * Perpendicular distance from line of force to pivot or axis.
What is a couple
An equal and opposite pair of forces applied to a body in parallel along different lines, causing the body to rotate without translational movement.
What is torque
The moment of a couple, calculated by one of the forces * perpendicular distance between forces.
What is the principle of moments
For a body in rotational equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of the clockwise moments about that same point.
What is density
Mass per unit volume of a substance
How to find density of an object
Using a digital balance to find the mass. Use a measuring cylinder to find the volume of a liquid. Calculate the volume of a regular shaped object by measuring its sides, using a ruler, a digital calliper or micrometer. Calculate the volume of an irregular object by placing it into a body of water in a measuring cylinder then measuring the change in water levels.
What is pressure
Force per unit cross sectional area.
How does pressure in water work
An object immersed in a column of fluid experiences pressure due to the weight of the fluid above it. The pressure at the base of a column of fluid is given by the equation p=hpg. At the base, the force is the weight of the fluid, so mg/A equals pressure. Mass is equal to density * volume, therefore pgV/a equals pressure. Volume divided by area equals height, therefore hpg = P
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. The pressure at the bottom surface of the object is greater than at its top surface. An object will sink if the upthrust acting up is smaller than the weight acting down. For a floating object, the weight is equal to the upthrust, so the object’s weight is equal to the weight of the fluid it displaces.
