Chapter 4 - forces in motion Flashcards
6 forces that could be on a free body diagram
Weight, friction, tension, drag, normal force, human force
What to do with the arrows on a free body diagram?
Point them all away from the centre of mass
Free body diagram
Shows the forces acting on an object from its centre of mass
How to find the acceleration down the ramp where you know the angle of the ramp from the ground
- Draw the acceleration due to gravity acting downwards from the object on the ramp
- Make a right angle triangle with g, the ramp and a line perpendicular to the ramp so that g is the hypotenuse
- The angle between g and the ramp is (90 - the angle from the ground to the ramp)
- Use trig to find the component
Turning Moment
Force x perpendicular distance
Nm = N x m
The force must be resolved to be perpendicular to the surface
Principle of moments
Clockwise moment = anti-clockwise moment when a body is in equilibrium
How to find the force acting on each of 2 pivots?
- Find the moment around the other pivot
2. Divide by the distance between them to find the reaction force
A force with a component upwards
A lift force
A force with a component forwards
A thrust
A force with a component backwards
A drag force
What does trebling the speed do to the drag force?
It multiplies it by 9
Drag force is directly proportional to speed squared
Graph of v/t of a falling object with no parachute
Increases velocity with decreasing acceleration until it plateaus at terminal velocity
Density
Mass (kg) / Volume (m^3)
Pressure
Force (N) / Area (m^2)
How to make an object rotate around a point without accelerating in a line?
Apply two equal and opposite forces, a “couple”
Turning effect of a couple
The torque
Torque equation
Average force x distance between forces
Pressure in a fluid
depth x density x acceleration due to gravity
In which direction(s) does pressure in a fluid act?
Equally in all directions
Archimedes’s Principle
If an object is partially or fully submerged, the upthrust is equal to the weight of fluid displaced.
How to find the upthrust on an object?
The difference between the forces at the top and bottom of the object
Change in depth x density x acceleration due to gravity x area
Torque
One of the forces multiplied by the perpendicular distance between them
How goes gps work?
- uses radio waves emitted by multiple satellites
- Multiply the speed of light by the time taken for the receiver to receive them to find the distance from each satellite
- there is a circle of points that distance from each satellite, the intersection of the circles is its location
Resultant force of a couple
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