Unit 2 - Forces and Newton's Laws Flashcards
What is an external force
Force originating from outside of an object
What is Newton’s first law
An object remains at rest or if in motion at a constant velocity unless acted on by a net external force
Summarise Newton’s first law
No resultant force = no acceleration
What is Newton’s second law
Acceleration is proportional to the net force and inversely proportional to the mass
Equation from Newton’s second law
F = ma
What is Newton’s second law
If object A exerts a force on object B then object B must exert a force of equal magnitude and opposite direction back on object A`
What is weight
What is the equation for determining weight
The force of gravity
W = mg
What is g
What can we approximate it to
9.81
10
What is mass
The measure of inertia of an object
_______ is constant but __________ changes due to differences in gravity
Mass
Weight
What is a normal force
Force exerted by surfaces to prevent solid objects pushing through one another
Forces PERPENDICULAR are
Normal
Forces PARALLEL are
Frictional
Give an instance where the normal force may not equal mg
When contact forces are not horizontal or there are extra vertical forces present
When are frictional forces present
When two surfaces are sliding over one another
Frictional forces are characterised by
The frictional coefficient
U
What is the equation connecting frictional force and the normal force
Define the terms of this equation
Ff = u . Fn
Ff = frictional force u = frictional coefficient Fn = normal force
What is static frictional force
Between a static object and the surface that it is resting on
What equation must be used to determine the MAX force required to move an object
Define the terms of this equation
Fmax = u . Fn
Fmax -force required to move
u - frictional coefficient
Fn - normal force
If you apply a force above Fmax what is seen
Kinetic frictional force will be exerted on it
What is the equation for determining the kinetic frictional force
Fk = u . Fn
Where Fk = kinetic frictional force
u = friction coefficient
Fn = normal force
Is there any static frictional force for a moving object
NO
Instead we would have kinetic frictional force
For an object on an incline plane which is not moving what term would give the normal force
Mg cos theta = N
Define tension
The force exerted by a rope/cable is the force of tension T
Tension is only able to
Pull
Steps for calculating tension in a system
1) draw forces acting on the object
2) write down F=ma for direction of tension
3) solve
Cos 60 =
0.5
