P8 Forces in Balance Flashcards
Displacement
Is a distance in a given direction
How can vector quantities be represented
With and arrow in the dorection of the vector and the of length in proportion to the magnitude of the vector
What can forces do to an object
Change its shape
Change its motion or its state of rest
Unit for force
N, newtons
Contact force
A force that acts on an object only when the objects touch each other
Non-contact forces
A force that is required to physically touch another object to act upon it
Contact force examples:
Friction
Air resistance
Stretching force (or tension)
Normal conatct forces
Non-contact forces examples:
Magnetic force
Electrostatic force
Force of gravity (gravitational field strength)
Newton’s third law
States that when two objects interact with each other, they exert equal but opposite forces on each other
What do you say if resultant force is zero
That all forces acting upon it are balanced
Resultant force
A single force that has the same effect as all the forces acting on an object
What’s a Free body force diagram
It shows all the forces acting on an object without any other objects or other forces shown
Newton’s first law of motion?
States that if the forces acting on an object are balanced the resultant force on the object is zero and of the object is at rest is stay stationary, but if it moving, it keeps moving at a constant speed and in the same direction
If two forces act on an object along the same line, the resultant force is:
Their sum, if the forces act in the same direction
Their difference, if the foces act in opposite directions
In this example, when using a spanner: the turning effect of the force, called the moment of the force, can be increased:
Incraeing the size of the force
Using a spanner with a longer handle (increase the distance)
Whats the Moment of a force?
A measure of the turning effect of the force on an object
Equation for moment of a force about a pivot?
M= F x d
d (perpendicular distance from the line of action of the force to the pivot)
F (force applied to the pivot)
How to Increase moment of a force
Increase force
Or distance
What can be used to exert a force that is greater than the effort
A lever (crowbar). Levers used in this way are known as force mulitpliers because the effort moves a much bigger load
Centre of mass
(Of an object) is the point at which its mass can be thought of as being concentrated
What happens if you suspend an object and then release it?
It will sooner or later come to rest with its centre of mass directly below the point of suspension. The object is then in equilibrium, which means it is at rest. Its weight doesn’t exert a turning effect on the object, because its centre of mass is directly below the point of suspension
What happens of the object is turned from its suspended position and then released?
It will swing back to its equilibrium position, because the weight has a turning effect that returns to object to equilibrium
When would you say and object is ‘freely suspended’?
If it returns to its equilibrium position after the turning force is taken away
Where is the centre of mass of a symmetrical object?
Along the axis of symmetry
Where’s the Centre of mass on a uniform ruler
At its midpoint
What would you say if the object at rest doesn’t turn
The sum of the anticlockwise moments about any point = the sum of the clockwise moments at any point
W1d1=W2d2
What determines wether the moments acts clockwise or anticlockwise?
The direction of the force and the position of the fixed point
What are the parallelogram of forces
A scale diagram of two force vectors
What is the parallelogram of forces used for
To find the resultant of two forces that do not act along the same line
What is required when calculating the parallelogram of forces?
A protractor a ruler and sharp pencil
What is the resultant in the parallelogram of forces
The resultant is the diagonal of the parallelogram that stars and the origin of the two forces
What does resolving a force mean
Finding perpendicular components that have a resultant force that is equal to the force
How to resolve a force into perpendicular directions
Draw a rectangle with adjacent sides along the two directions so that the diagonal represents the force vector
What can be said about an object in equilibrium
The resultant force is zero
Why is an object at rest in equilibrium
Because the resultant force on it is zero
