Mechanics Flashcards
What is the difference between mass and weight?
Mass is scalar and not dependent on gravity acting upon it
Weight is vector and dependent on gravitational field strength
If an object is in equilibrium, it means the object is….
Not accelerating so is either:
-stationary
-moving at a constant velocity
How can forces acting on an object be shown to be in equilibrium?
-Adding horizontal and vertical components of the forces acting on it, showing they equal 0
-If there are 3 forces acting on the object draw a scale diagram -> closed triangle = equilibrium
What is a moment?
A turning force: force multiplied by the perpendicular distance from the point to the line of action of the force
What is meant by a couple?
A pair of equal and opposite coplanar forces
What is meant by the centre of mass?
The point at which all the mass of an object acts
For a uniform object the centre of mass is the centre of the object
If you have a uniform object, where would its centre of mass be?
At the centre of the solid
What is the area under a velocity-time and acceleration-time graph?
The displacement travelled and the velocity respectively
As speed increases, air resistance…
Increases (proportional to the square of speed)
A ball is projected off a castle at 6 m/s, how does its horizontal velocity change from its launch until it hits the ground?
Horizontal velocity stays the same -> no acceleration in that direction
How do SUVAT equations reflect that all objects fall at the same rate?
Mass is not included in SUVAT -> mass of an object doesn’t affect its speed or acceleration
In projectile motion, what is vertical acceleration?
Vertical acceleration + gravitational field strength
What is meant by terminal velocity?
When forces acting on a falling object become balanced
Acceleration becomes 0, and object is moving at max. velocity
What is meant by friction?
A resistive motion between an object and a surface or an object moving through a fluid
Acts in the opposite direction to the movement
What is Newton’s 2nd law?
Acceleration is proportional to force
F=ma
What is Newton’s 1st law?
An object stays moving at a constant velocity until an external resultant force acts upon it
What is Newton’s 3rd law?
If an object A exerts a force on object B, Object B will exert an Equal but opposite force on object A
What is the principle of moments?
When a body is balanced
total clockwise moments = total anticlockwise moments (about the same point)
How do you find a resultant vector?
How you do it in maths. Add the two vectors and use Pythagoras.
You need a bearing too.
A Remote controlled aeroplane flies with a velocity 14ms-1 east with an 8.0ms-1 wind north. Find resultant vector
142 + 8.02 = R2 so root answer = 16.124
Use tan-1(8.0/14) to find angle of 30º
Barings are measured from the north so 90-30 = 060
What is a free-body diagram?
A single body on its own showing all the forces acting on IT but not the forces it exerts on the rest of the world.
Define equilibrium
If an object is in equilibrium there is no resultant force
There are also no resultant moments
Explain how a lever works
A lever increases the perpendicular distance from a turning point / pivot so with the same force you get a larger moment.
What is a couple? What makes them special?
a pair of forces equal in size but acting in opposite directions. A couple causes no resultant linear force but does produce a moment.
