Forces Flashcards
What happens to the velocity if the resultant force is zero (Newton’s first law)
It is at a constant speed
What is Newton’s third law?
When two objects interact with each other they exert equal and opposite forces on each other
Hooke’s law
Force applied= spring constant x extension
What is a moment
The size of the force (moment) depends on the effort (force applied) and the perpendicular distance from the line of action of the force to the pivot (length of the lever)
How to calculate the moment
Moment of force= force x perpendicular distance from line of action of force to the pivot
M = f x d Nm = N x m
Force equation (newton’s second law)
Force= mass x acceleration
Scalar vs vector
Vector has a magnitude and direction, scalar just a magnitude
Gravitational force
Gravity is the force of attraction between masses, weight is mass x gravity
Resultant force
The single force with the same effect as each individual force acting on it
It means that energy is transferred and work is done
Work done=
Force x distance
How to find the resultant force of forces not in opposite directions
Draw all the forces acting on an object
Draw a straight line from the start of the first force to the end of the last
Measure length for magnitude and angle for direction
Can use Pythagoras
Equilibrium
If the forces give a resultant force of 0
Stretching, compressing and bending
Need more than one force
Elastically deformed if it can return to the same shape when the force is removed
Inelastically deformed if it can’t return
Work is done and energy transferred to elastic potential
Force=
Spring constant x extension
Until the limit of proportionality when the graph starts to curve
Hooke’s law
Elastic potential energy
Elastic potential energy = 1/2 spring constant x extension 2
Moment
The turning effect of the force
Moment = force x perpendicular distance from line of action to action of the force
Gears
Interlink so turning one causes another to turn in the opposite direction
Transmit the rotational effect from one place to the other
Force to larger gear has bigger moment
Fluid pressure=
Force/Area
Pressure in a liquid depends on
Depth and density
Pressure = depth x density x gravitational field strength
What force is from objects in fluids
The pressure exerts a force in every direction
Pressure increases with depth
Causes an upwards resultant force (upthrust)
Upthrust= weight of fluid displaced
How does an object float
If weight is less than upthrust
So there is an upwards resultant force
Walking, running, cycling speeds
1.5 m/s
3 m/s
6 m/s
Car, train, plane speeds
25 m/s
55 m/s
250 m/s
What affects travel speed
Fitness, age, distance terrain
