Physics Unit 1 Force Force push or pull

Physics Unit 1 Force

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

Newton • metric unit of force • named in honor of Sir Isaac Newton

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 • force of attraction between all objects in the universe

Gravity • the larger an object’s mass, the greater the gravitational force

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/d 2

What is air resistance? • air resistance • force that opposes the movement of an object in air

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

Types of Friction • Static friction – friction of an object at rest

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 is the amount of force acting on a surface

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

Fluid Pressure • pressure in gases and liquids

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

Air Pressure • air pressure changes with altitude • the higher you are, the lower the air pressure

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

Bernoulli’s Principle • three forces combine to help an airplane fly • the upward force on a plane’s wing is called lift • a forward force, or thrust, helps the plane take off and maintain air speed • the air resistance on a plane is called drag