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FORCE = Any push or pull which causes something to move or change its speed or direction
What is a Force?
Forces can be BALANCED or UNBALANCED
Balanced forces are equal in size and opposite in direction
UnBalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results.
What is a Force?
Can you think of examples of forces?
Balanced Forces?
Unbalanced Forces?
What is a Force?
Force
I. ForceA. a push or pull that one body exerts on
anotherB. What forces are being
exerted on the football?
Fkick
Fgrav
Measuring Forces
I. Forces are measured in newtons (kg . m/s2).
I. Forces are measured using a spring scale.
Force
I. Balanced Forces
A. forces acting on an object that are opposite in direction and equal in size
B. no change in velocity
Force
I. Net Force
A. unbalanced forces that are not opposite and equal
B. velocity changes (object accelerates)
Ffriction
W
Fpull
Fnet
NN
ConcepTest 2You are a passenger in a car and not wearing your seat belt.
Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door.
Which is the correct analysis of the situation? ...
ConcepTest 2
1. Before and after the collision, there is a rightward force pushing you into the door.
2. Starting at the time of collision, the door exerts a leftward force on you.
3. both of the above
4. neither of the above
2. Starting at the time of collision, the
door exerts a leftward force on you.
ConcepTest 1
TRUE or FALSE?
The object shown in the diagram must be at rest since there is no net force acting on it.FALSE! A net force does not cause motion. A net force causes a change in motion, or acceleration.
Taken from “The Physics Classroom” © Tom Henderson, 1996-2001.
GRAVITYGRAVITY: An attraction force between all masses
Newton’s universal law of Newton’s universal law of gravitationgravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe
The amount of gravitational force depends upon the mass of the objects and the distance between the objects
What is Gravity?
The greater the mass, the greater the forceforce
The greater the distancedistance, the lessless the force
Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2
What is Gravity?
Gravity
A.force of attraction between any two objects in the universe
B.increases as...
1.mass increases2.distance decreases
Gravity
I. Who experiences more gravity - the astronaut or the politician?
less distance
more mass
I. Which exerts more gravity - the Earth or the moon?
Gravity
I. Would you weigh more on Earth or Jupiter?
greater gravity
greater weight
greater mass
A. Jupiter because...
What is Motion?
Motion: A change in position of an object compared to a reference point
What is Friction?Friction = A force that opposes or
slows down motion Caused by the physical contact
between moving surfaces The amount of friction depends
upon the kinds of surfaces and the force pressing the surfaces together
Changes motion into heat
FrictionA. force that opposes motion
between 2 surfacesB. depends on the:
1. types of surfaces2. force between the
surfaces
FrictionI. Four Types of Friction
Static Friction – force that acts on objects that are not moving. (Couch Potato)
Sliding Friction - force that opposes the direction of motion of an object as it slides over a surface. (Ice skating or bobsledding)
Rolling Friction – friction force that acts on rolling objects. (Rollerblading)
Fluid Friction – force that opposes the motion of an object through a fluid. (Planes flying or submarines traveling)