Forces and Motion All forces have a magnitude and direction

Forces and Motion  All forces have a Magnitude  A.k.a. Strength  All forces have a Direction  All forces have a Magnitude  A.k.a. Strength  All forces have a Direction

Forces and Motion  Force – A push or pull on an object  Net Force – The summation of all forces acting on a single object  Adding and subtracting their magnitudes and directions  Net Movement – The result of the net force (how the object moves)  Force – A push or pull on an object  Net Force – The summation of all forces acting on a single object  Adding and subtracting their magnitudes and directions  Net Movement – The result of the net force (how the object moves)

Forces and Motion  Forces can be added and subtracted to get a Net Force  Net Force > 0 - change in movement  Net Force = 0 - no change in movement  The key here is the CHANGE in motion Objects can be in motion with a negative net force Objects can be in motion with a net force of zero  Forces can be added and subtracted to get a Net Force  Net Force > 0 - change in movement  Net Force = 0 - no change in movement  The key here is the CHANGE in motion Objects can be in motion with a negative net force Objects can be in motion with a net force of zero

Forces and Motion Objects can be in motion with a negative net force  Example:  I kick a ball with 50 newtons of force straight forward.  What is the net force as I kick?  What is the change in direction?  After I kick the ball, the force that I am inputting becomes 0. This means that only gravity and friction are acting on the ball.  What is the net force now?  Does the ball immediately stop?  Does the ball stop eventually? Objects can be in motion with a negative net force  Example:  I kick a ball with 50 newtons of force straight forward.  What is the net force as I kick?  What is the change in direction?  After I kick the ball, the force that I am inputting becomes 0. This means that only gravity and friction are acting on the ball.  What is the net force now?  Does the ball immediately stop?  Does the ball stop eventually?

Forces and Motion Objects can be in motion with a net force of zero  What slowed down and eventually stopped the ball in the previous example?  Example:  Imagine we are in space. In fact, imagine we are on the surface of the space station and I decide to throw a rock with 20 newtons of force away from Earth.  What is the net force acting on the rock as I throw it?  After I throw it my input of force is 0, however because we are in a vacuum (no air) and away from a planet (no gravity) there is NO force acting on the rock.  What is the net force now?  Will the rock stop moving because the net force is zero? Objects can be in motion with a net force of zero  What slowed down and eventually stopped the ball in the previous example?  Example:  Imagine we are in space. In fact, imagine we are on the surface of the space station and I decide to throw a rock with 20 newtons of force away from Earth.  What is the net force acting on the rock as I throw it?  After I throw it my input of force is 0, however because we are in a vacuum (no air) and away from a planet (no gravity) there is NO force acting on the rock.  What is the net force now?  Will the rock stop moving because the net force is zero?

Forces and Motion  So what are the rules?  IF …there is friction, net force of 0 is impossible because friction will always be slowing it down.  Therefore, net force will be negative.  IF …there is no friction, net force of 0 means it will continue moving at the same speed until something (wall, person, planet) stops it.  Therefore, if it is stated that the net force is 0 you can assume there is no friction.  So what are the rules?  IF …there is friction, net force of 0 is impossible because friction will always be slowing it down.  Therefore, net force will be negative.  IF …there is no friction, net force of 0 means it will continue moving at the same speed until something (wall, person, planet) stops it.  Therefore, if it is stated that the net force is 0 you can assume there is no friction.

Forces and Motion  Friction – the force felt between two objects when one or both is in motion  Drag – the same as friction, but in the air or liquids  Swimmers  Airplanes  Baseballs  Birds  Fish  Friction – the force felt between two objects when one or both is in motion  Drag – the same as friction, but in the air or liquids  Swimmers  Airplanes  Baseballs  Birds  Fish

Forces and Motion  Types of Net Force  Balanced Force – when two (or more) forces acting on an object are equal and cancel each other out  No movement  Unbalanced Force – when one force acting on an object is greater than the other  Movement  Types of Net Force  Balanced Force – when two (or more) forces acting on an object are equal and cancel each other out  No movement  Unbalanced Force – when one force acting on an object is greater than the other  Movement

Forces and Motion  Balanced and Unbalanced

Forces and Motion  Relative Motion – one objects motion compared to another  What is the Relative Motion if…  Two people are walking in the same direction at 2 mph?  Two cars are traveling in opposite directions at 40 mph?  A person is walking at 3 mph while another is driving past them at 30 mph?  Am I moving right now?  Yes, the earth is moving at 67,000 mph!! …but so am I so it feels like nothing  Relative Motion – one objects motion compared to another  What is the Relative Motion if…  Two people are walking in the same direction at 2 mph?  Two cars are traveling in opposite directions at 40 mph?  A person is walking at 3 mph while another is driving past them at 30 mph?  Am I moving right now?  Yes, the earth is moving at 67,000 mph!! …but so am I so it feels like nothing

Forces and Motion  Force Diagrams!!

Forces and Motion  Force Diagrams!!  Is this balanced or unbalanced?  What is the net force?  What direction will the block travel?  Force Diagrams!!  Is this balanced or unbalanced?  What is the net force?  What direction will the block travel?

Forces and Motion  Force Diagrams!!  Is this balanced or unbalanced?  What is the net force?  What will happen?  Force Diagrams!!  Is this balanced or unbalanced?  What is the net force?  What will happen?

Forces and Motion  Objects NOT in motion  Are there forces acting on this book?  Objects not in motion still have forces acting on them.  Objects NOT in motion  Are there forces acting on this book?  Objects not in motion still have forces acting on them.

Forces and Motion