Projectile Motion And Forces Pressure, Density Flashcards
Projectile motion is:
Refers to an object that is in flight after bring thrown or projected.
Acceleration in projectile motion :
Acting in vertical direction which is acceleration due to gravity
No acceleration in horizontal direction hence constant speed.
To find vertical and horizontal components :
Use equations of motion separately applied in x and y axes to get unknown parameters
Vertical component of velocity _ going up the parabola, at _ point of path becomes _
Decreases
Highest
0
Angle between velocity (horizontal) and acceleration (due to gravity) at highest point is
90°
Gravitational field:
Provides force of attraction between masses
Uniform gravitational field :
Field lines parallel, same distance apart
Force depends on _ and _ which vary with planet
Mass and strength of gravitational field
Electric field:
Provides force of attraction/repulsion between charges
Fields equations :
F=mg, g is gravitational field strength
F=Eq, E is electric field strength as
Force depends on _ and _ (electric)
Size of charge and strength of E
Similarities between G and E fields
- point charges and masses follow inverse square law
- non contact forces ie exert force from distance
- field strength defined in terms of force per unit N/kg or C
Differences between G and E fields
- G can only be attractive while E be both attractive and repulsive
- objects can be shielded from E but not G
- E only act upon charted masses, G on all masses
What is upthrust
Force which pushes upwards on a object submerged in fluid ie liquid or gas
Upthrust is due to
Difference in hydrostatic pressure at top and bottom of immersed object
Upthrust/buoyancy is _ in liquid that gases, because _
Larger
Liquids are more dense
Upthrust/buoyancy is _ in liquid that gases, because _
Larger
Liquids are more dense
Hydrostatic pressure depends on _ that an object is submerged in from _. This means
Height/depth
P=pgh
Water pressure at bottom is greater than at top
Explain what happens for upthrust
Upthrust is directly proportional to pressure. Force at bottom will be greater than at top. Resultant pressure causes resultant upward force on object called upthrust
Object rises in fluid when _. Objects float when _
Upthrust is greater than weight
Objects density less than that of fluid
Upthrust is influenced by _ not _
Pressure
Not density
Drag force is
Force acting the opposite direction to an object moving through fluid
Key component of drag :
Increase with speed
Centre of gravity
Point at which weight of object may be considered to act (seems)
For symmetrical objects with uniform density where is centre of gravity located
Point of symmetry
2 factors affecting stability
-objects more stable when centre of gravity lies above base
-wider the base lower centre of gravity hence more stable
(centre of mass should be over base when crossed will topple)
What does and does bot depends on gravitational field
Centre of gravity does - W=mg where g is acceleration due to gravity
Of mass doesn’t
Centre of gravity of an object in space will be :
More towards object with larger gravitational field
Centre of gravity is a _ and changes with _
Hypothetical point
Shape of body
Moment is
Turning effect of a force. It is force multiplied by perpendicular disgrace from pivot
Moments occur when
Force causes object to rotate about pivot
SI unit for moment
Nm
Greater the - largee the moment with less - being applied
Distance
Force
What is a couple?
Pair of forces acts to produce rotation only.
Moment of a couple :
Doesn’t depends on pivot, rather the perpendicular distance between the 2 forces
Couple has pair of forces that are:
- equal in magnitude
- opposite in direction/parallel
- perpendicular distance between them
Condition of couple
- produce resultant force 0, so F=ma and no acceleration
- lines of actions of forces don’t meet
Turning effect or moment of couple called
Torque
Turning effect or moment of couple called
Torque
When line of action goes through pivot…
Perpendicular distance becomes 0
No moment
Not a couple
Torque =
One of the forces × perpendicular distance between forces
Principle or moments:
For a system to be balanced or in equilibrium, sum of clockwise moments about a point must be equal to sum on anticlockwise moments about the same point
When a system is in equilibrium :
-no resultant force
-no resultant torque
Remains at rest or at constant velocity. No rotation
In equilibrium, coplanar forces are representated using
Closed Vector triangles. Form closed path where they follow each other
