Chapter 4 - Force, Mass And Weight Flashcards
Define the centre of mass
The centre of mass of an object is the mean point of all the mass of an object
Define the centre of gravity and where is it?
The centre of gravity is the point where the entire weight of an object can be thought to be concentrated. (Appears to act). It is in the same place as the centre of mass.
How can you find the centre of gravity of an object?
By using 2 points of suspension on a 2D object (flat object) you can use a plumb line to draw a vertical line across the object. The point of intersection of these two lines is the centre of gravity.
What are the 6 main forces to be considered in almost any free-body diagram?
Weight
Friction
Drag
Tension
Upthrust
Normal
What are the two main factors in causing an objects terminal velocity?
The objects speed and cross-sectional area
What is drag directly proportional to?
Speed^2
What is the equation for the moment of an object?
Moment = force x distance perpendicular to the direction of the line of action of the force
What is the unit for a moment?
Nm (Newton metre)
Define a couple of forces
When two equal forces parallel to each other but on different lines that are of equal magnitude affect two different sides of an object causing it to spin without moving (rotating and not translating)
What is the torque of a couple?
The torque of a couple is the moment between the pair of forces
What is the equation for the torque of a couple?
Torque (Nm) = Force (N)(of one of the forces) x distance (m)(between the two forces not the centre)
What needs to be included alongside the answer and units for a question that wants the torque of a couple?
The direction of motion of the torque (clockwise or anti-clockwise)
What is an easy way to help visualise and thus solve a triangle of forces question?
Draw the completed triangle of forces
What is the equation for pressure? (Basic)
P = F / A
What is the unit for pressure and what is its unit in SI units?
Pascals (Pa) or (Nm^-2)
What is the equation for the pressure of a vertical column of liquid?
P = height x density x g
What unusual property is true about the pressure in a fluid?
The pressure at any particular depth is the same in all directions.
What is the equation for the upthrust of an object underwater and how is this obtained?
Upthrust = x (depth of the object) * cross sectional area * density of the fluid * g
This is obtained by subtracting the pressure acting at the top of any object from the pressure acting at the bottom of the object. This is what gives x as distance and not depth since x is the distance between the two places that the pressure is being measured.
What is the Upthrust of an object in a fluid equal to?
The weight of the the fluid displaced by the object
What is archimedes principle?
The Upthrust exerted on a body immersed in a fluid wether fully or partially submerged is equal to the weight of the fluid that the body displaces.
What could you change in the ball and tube of liquid experiment to affect the balls terminal velocity?
Change the liquid
Change the size of the ball
Change the shape of the item being dropped
Change the mass of what’s being dropped
What is Archimedes principle?
When a body is partially or fully submerged in a fluid, it experiences an upthrust equal to the weight of the fluid displaced
