Forces Notes
4 Fundamental Forces Gravity - attraction of objects for each other Electromagnetic force – friction is an example Strong nuclear force – holds protons together in atoms’ nuclei Weak nuclear force – holds electrons near nucleus
Field Forces & Contact Forces Field Forces – no touching required examples: magnetism, gravity Contact Forces – touching required examples: pushing, pulling, sliding
Field Forces – MagLev Trains
Maglev http://www.youtube.com/watch?v=weWmTldrOyo
Types of contact forces Require objects to touch each other Types of contact forces Forces can be defined as a push or pull. Passing a basketball or kicking a soccer ball are both examples of applying a force to an object.
Forces Affect How Objects Move: Change an object’s shape Start an object moving Cause an object to move faster Cause an object to move slower Cause an object to stop Cause an object to change direction Forces Affect How Objects Move:
More on Forces: Forces are measured in Newtons (N) Forces usually act in pairs. Forces act in specific directions. Forces are vectors Forces are represented using arrows Forces usually can not be seen. Only their effects can be seen.
What happens when a force acts on an object? Depends on STRENGTH and DIRECTION of the force. Depends on whether the forces are balanced or unbalanced. Balanced – no change in motion Unbalanced – change in direction of greatest force. Try the following examples….
Which direction does the box move? Balanced or unbalanced? PUSH PUSH Remember, larger arrows represent larger force. The box will move in the direction with the most force
Which direction is this box moving? Balanced or Unbalanced? PUSH PUSH
What about this box? Balanced or Unbalanced? PULL PUSH
What direction does this box move? Balanced or Unbalanced? PUSH PUSH
What direction does the ball roll? Balanced or Unbalanced? PUSH PULL
The magnitude of the force is measured in Newtons (N) The magnitude of the force is measured in Newtons (N). This can help in measuring the strength of the force …. Newtons (N)! Unit of measurement for Force!!
Which direction is the ball rolling Which direction is the ball rolling. What is the Magnitude of this force? PUSH PUSH 4 N 1 N
What is the direction and magnitude of the force causing the face to move? PULL PUSH 5N 1N
NET FORCE NET FORCES TWO FORCES COMBINE When two or more forces act on an object at the same time. The forces combine to form a NET FORCE 4N 1N 3N NET FORCE TWO FORCES COMBINE
CAN COMBINE IN OPPOSITE DIRECTIONS
BALANCED FORCES BALANCED FORCES OCCUR WHEN THE NET FORCE EQUALS ZERO PUSH PUSH 3N 3N
Opposing forces in action
Newton’s Laws of Motion First Law: “An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force.” An object at rest tends to stay at rest. An object in motion tends to stay in motion unless acted on by a net force http://www.youtube.com/watch?v=cuG8sIiV8iQ&feature=fvwrel
The First Law and Inertia Inertia – the tendency of an object to resist a change in motion unless an outside force acts on the object. Example: Riding in a car, driver slams on the brake, purse on the seat slides to the floor. http://youtu.be/8zsE3mpZ6Hw
Newton’s Second Law “The unbalanced force acting on an object equals the object’s mass times its acceleration.” The unbalanced force on an object determines how much an object speeds up or slows down. Force = mass x acceleration f=ma
F=ma in action http://www.youtube.com/watch?v=iwP4heWDhvw
So... For equal forces, a larger mass accelerates less. The yellow ball went farther and faster than the red one. It’s easier to push a Smart Car than an Escalade.
Force is measured in Newtons One Newton = the force that gives the mass of 1 kg an acceleration of 1 m / s / s 1 N = 1 kg x 1 m/s/s 1 N = 0.225 lb 1 lb = 4.45 N
Force Problems Force = Mass x Acceleration Mass = Force Acceleration Acceleration = Force Mass UNITS: mass = kg acceleration = m/s² force = Newtons
Or instead of learning all three types of problems… just do a triangle!
Now Try Practice Problems