04 forces in action + 03 forces and motion Flashcards
What is a free body diagram?
A singular object with all its forces drawn on it.
What is the net force?
The vector sum of all forces acting on an object.
What is the general principe of the equation f=ma
A more massive objects requires more force to change the velocity.
What is intertia?
How hard it is to change the objects velocity.
What is weight?
A downwards force due to mass being in a gravitational field.
What is friction?
The force when two objects make contact with each other, it opposes Motion and acts in the opposite direction of movement.
What is drag?
It opposes the motion of an object while moving through a fluid.
What is upthrust?
An upwards force on an object in a fluid.
- depends on density
What is the normal contact force?
When two objects touch, it is constant and perpendicular to the surface.
What is tension?
The force that acts along a string/rope, thrust is the opposite of tension.
What is the centre of mass?
The point where the weight appears to act on an object.
Does the centre of mass of an object have to be inside the object?
No.
How do you find the centre of mass of a shape?
- Pin it up so it can hang freely
- Draw a line vertically downwards from where it hangs, use a plum to determine this
- Repeat this step minimum three times, all lines should intersect at the centre of mass
What is the formula for density?
mass/volume, m/v
What is the density of water?
1000kgm(-3)
What is the density of air?
1.3kgm(-3)
What is the formula for pressure?
force/area, f/a
What is the unit for pressure?
Pascals
What is the formula for density of a fluid above an object?
P(rho)=pgh
What is upthrust in terms of weight?
The weight of the fluid displaced by the object.
What is the formula for upthrust?
p(rho)gv
What is a moment?
a force that causes something to rotate.
What is the equation for a moment?
force multiplied by the perpendicular distance from the hinge.
What are the units for a moment?
Nm.
What is the principle of moments?
For an object at equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments.
How do you work out a moment when the force isn’t perpendicular to the hinge?
Split the force vector up to find the perpendicular distance.
What is a couple?
Two forces of equal magnitude acting in opposite directions, not acting along the same line.
What is the equation and unit for torque?
Force multiplied by distance, measured in Nm
How do you find the torque of a couple?
One of the forces multiplied by the distance between them.
What is the simplified definition for torque?
The rotational force that causes and object to turn or twist.
When does triangle of forces apply?
When there is 3 forces acting on an object.
What are the methods of solving triangular forces problems?
- Nose to tail diagrams
- Finding the horizontal and vertical components of the vectors
