physics unit 1 force. force – push or pull a force always acts in a certain direction ex. if you...
TRANSCRIPT
Force – push or pull
• A force always acts in a certain direction• ex. if you push something, the force is in the
direction of the push
• To describe a force you need to know direction and strength (size) of the force
• ex. Push the box to the right with a force greater than 20 N
Net force
• Is the total force acting on an object
• To find net force:• Add forces acting in the same
direction• Subtract forces acting in opposite
directions
Weight
- Weight is a force- Weight is a measure of the amount
of gravity acting on an object- To lift an object on Earth you must
over come the gravity pulling on it, you must lift with a force equal to or greater than its weight
What is gravity?
• Sir Isaac Newton• 1642 – 1727• The Law of Gravity or Universal
Gravitation – states that all objects are attracted to each other by the force of gravity
Gravity
• the greater the distance between two objects, the smaller the gravitational force• the force of gravity decreases by the
amount equal to one divided by the distance (d) squared• 1/d2
Air Resistance
• a larger surface area usually results in greater air resistance
• lighter objects feel more air resistance than heavier objects
Terminal Velocity
• speed at which air resistance and gravity acting on an object are equal• as an object falls, it’s speed increases
at a steady rate until it reaches it’s terminal velocity
Vacuum – empty space
• In a vacuum there is no air and no air resistance
• in a vacuum, all objects fall at the same speed
What is friction?
• Friction• force that opposes the motion of an
object• the force of friction works in the opposite
direction of the force of motion
Types of Friction
• Sliding Friction• the source of friction is the contact
between two surfaces, at least one of which is in motion
Types of Friction
• Rolling Friction• friction between two surfaces that are
not in constant contact• ex. wheels
Types of Friction
• Fluid friction – friction that occurs when an objects move through a fluid; through a gas or liquid
Types of Friction
• Air Resistance is a Type of Fluid Friction• friction results from air pushing on an
object as it is moving
Friction
• friction makes motion possible
• friction also makes it hard to move objects
• reducing friction makes it easier to move objects
How can friction be reduced?
• by changing sliding friction into rolling friction
• by using lubricants• Lubricants – substances that reduce
friction
Pressure
• pressure can be changed by changing the amount of force acting on an area
• pressure can be changed by changing the area on which a force acts
Air Pressure
• air pressure is caused by the motion of particles in the air
• you do not feel the weight of the air because the pressure inside your body is equal to the air pressure around you
What is Bernoulli’s principle?
• Bernoulli’s Principle• principle that states that as the speed
of a fluid increases, its pressure decreases
Bernoulli’s Principle
• airplane wings are designed to use Bernoulli’s principle• air traveling over the wings moves
faster than air underneath• this reduces the pressure on top of
the wing, allowing it to be pushed upward