Module 3 Dynamics Flashcards
What are the four fundamental forces?
Gravitational force
Electromagnetic force
Strong nuclear force
Weak nuclear force or weak interaction
What is weight
the gravitational force acting through a centre of mass
What is friction
force that arises when two surfaces rub against each other
Friction always acts in opposite direction to velocity
What is drag?
resistive (frictional) force of an object travelling through an fluid
Drag in opposite direction to velocity
What is tension
force within a stretched rope or cable
What is normal contact force?
the force arising (perpendicular to the surface) when one object rests on another
Which factors effects drag?
- Velocity - higher the v higher the drag
- Cross sectional area - more streamlined the object reduces drag (less contact surface area)
- Roughness of the surface area of the moving object
- Viscosity of the fluid
What does F refer to in Newton’s 2nd law?
Resultant force (or net force)
What are base the unit for Newtons?
kg*m s^-2
How to calculate resultant force in newtons?
mass times acceleration
What does Newton’s second law in the form F=ma apply to?
objects with constant mass
Define a Newton
One Newton is the force that causes a mass of one kilogram to have an acceleration of one metre per second squared
When is the equation F=ma no longer applicable?
when an object is travelling near the speed of light
What is the effect on the mass of an object travelling near the speed of light?
mass increases
Calculate the acceleration, and thus describe the motion of an object with the mass of 80kg in a body of water with the upthrust of 500N
- Weight 80x9.81 = 784.8N
- weight>upthrust therefore resultant force (direction of motion) is vertically down
- U-W = ma
- acceleration = (500-784.8)/80 = -3.56ms^-2
- Both acceleration and velocity are down therefore object is traveling and accelerating down so getting faster
What is terminal velocity
when the resultant force of a moving object is 0
so constant velocity
When do objects reach terminal velocity when falling?
when the drag force is equal but opposite to weight, there is no acceleration
(ignoring drag but may be included sometimes)
What is a word used to describe an object moving at its maximum constant velocity?
terminal velocity
How to calculate the resultant force of an accelerating object?
forces in the direction of acceleration - forces in opposite direction
When an object is falling at terminal velocity, KE does not change but GPE does, explain what happens to this loss of GPE
GPE is converted to work done against drag as heat
KE constant (constant velocity)
GPE decreases if the object is falling
When drag due to air resistance is taken into account, why can suvat equations not be used?
acceleration is not constant
Describe the motion of a skydiver who jumps out of a plane and opens a parachute
(see velocity time graph in notes)
- Initially, only weight acts so a=g vertically downwards, no drag
- Drag increases with increasing speed, W>D acceleration downwards but decreasing
- Weight = Drag so resultant force = 0N, acceleration = 0. First terminal velocity
- Parachute opens, large drag force caused by increase in surface area
- Drag>weight so resultant force upwards, acceleration upwards and velocity downwards but decreasing
- 2nd lower terminal velocity W=D, RF=0N, a=0
Investigation on ball bearings through a viscous fluid
- a glass tube filled with a washing detergent
- insulating tape at equal distances across the tube
Re investigating velocity of ball bearings through a viscous fluid
How will the arrangement of the markers on the tube change when placing them at equal time intervals?
will get wider and wider until distance is same as terminal velocity is reached
Newton
force required to give a mass of 1kg an acceleration of 1ms-2 in the direction of the force.
Upthrust
upward force that acts on a body fully or partially submerged in a liquid or gas.
