forces
TRANSCRIPT
May the Force be with you
This is funny
Definition
Force: any push or pull on an object (it's that simple)
….But be careful! Commonly students will think
forces have to come from living or moving things. Not true. Gravity pulls a chair to the floor and the floor pushes back.
Forces can cause:
1) speeding up 2) slowing down 3) change in direction IN OTHER WORDS FORCES CAN*
CAUSE: ACCELERATION*(but they don’t always cause
acceleration!)
Balanced forces:
When all the forces cancel each other out= no net change in motion (no acceleration!)
Unbalanced forces:
Two or more forces that work and add together to change motion (cause acceleration)
Example of a canoe being rowed on a river on a windy day
http://rt210.sl.psu.edu/simulations/physlets/force_table.html
Vectors
Forces are vectors Vectors are ____________with
______________ Which one is a vector: Speed
or Velocity?
Newtons
In the metric system, the unit of force is the Newton.
It can be used to quantify the pull or push of ANYTHING!
What is correct: To weigh something in pounds, Newtons, or Kilograms?
balanced forces example:
You on a chair you are pulled down by gravity and
the chair pushes back on your butt. Think about it....If you sat on the hard chair for three hours without moving, wouldn't you feel the chair's push?
unbalanced forces example:
a rocket taking off
the force of the engines is enough to overcome gravity and the rocket accelerates off the launch pad
Questions
Is it possible to have one balanced force? If so, draw as a vector diagram.
Is it possible to have 2 balanced forces? If so, draw as a vector diagram.
Is it possible to have 3 balanced forces? If so, draw as a vector diagram.
More questions
Can an object be in motion with balanced forces acting on it? Defend your answer.
Can an object be stationary with unbalanced forces acting on it? Defend your answer.
More….
Can you predict the motion of this box?
Force: 5 N
Friction: a force; it causes negative
acceleration (slows things down and makes them stop) (Can it also aid positive acceleration?)
it's mostly caused by: interaction of the matter that is in contact
Also caused by differences in materials that are in contact.
The Three Types of Friction and Each One’s Properties
3 types Typical Relative strength
Examples
Sliding Strongest Book pushed on table
Rolling Medium Car wheels
Fluid Lowest Swimming or flying
From mass to Force (Part II)
Mass: Amount of Matter in an object Something is hard to move if it has more mass
Basically the “amount of stuff” found in something
Inertia
Objects with mass don’t like to move
This property is inertia
How is it measured?
Weight
Weight is a ___________ Caused by ___________ All atoms are pulled by gravity, so
things with atoms have weight
Speed and Velocity
Rate of motion Velocity includes direction V= D/T (with direction) Units: Meters per second
Momentum When things move faster, they become
harder to stop And when they are more massive they
are also harder to stop Momentum is like “inertia in motion” ρ=Mass times velocity Momentum is not a force, but it takes a
force to stop momentum……… Units: Kilogram Meters per second
Acceleration
When speed or direction changes Only a force can cause acceleration Change in speed divided by time Or Ending speed – Starting speed TimeUnits: Meters per second squared
Acceleration when falling
On earth this is at a rate of 9.8 m/s/s
This is a fast rate of acceleration
What affects this acceleration during the fall?
Finally………Force
Any push or pull Forces can accelerate a mass Force equals mass times
acceleration F= MA Units: Kilogram meters per second
squared (or Newtons)
Weight is a Force On earth you calculate weight byMultiplying mass (in Kg) times
acceleration due to gravity (9.8 m/s/s)
This will give you weight in Newtons Weight= mg If you wanna turn your mass into
weight….don’t forget to multiply by 9.8 (m/s/s)