Forces Use the force

FORCE What is force? –No, Obi Wan it is not some mystical force that surrounds us and binds us to the universe. It surrounds us.. binds us… Brings us together.

FORCE Any push or pull where one body exerts another –Pushing, pulling, stretching, squeezing, etc… Usually measured in Newtons (N) Measured with a Scale

Two Effects of Forces 1.Balanced Forces 2.Unbalanced Forces

Balanced Forces there is no change in movement. –Example : Two football players push with the same force against each other. –also called equilibrium-

Unbalanced forces -Unbalanced forces result in a change in movement also called net force

Example: There are 2 football players pushing against each other. One pushes with 50 N and the other pushes with 75 N. What is the net force?Example: There are 2 football players pushing against each other. One pushes with 50 N and the other pushes with 75 N. What is the net force? 75 – 50 = 25 N What if they pushed together?

Friction Force that opposes motion between two surfaces The amount of force depends on: –Kind of surface –Force pressing surfaces together

Friction Some examples of friction? Friction can be both harmful and beneficial

GRAVITY

Gravity A force that every object in the universe exerts on every other object. It is often too slight to notice Example: The force between your hand and your book. There is one there, but you can ’ t feel it. When CAN you feel gravity?

Gravitational Force The amount of a gravitational force between two objects depends on: –Mass of the objects –Distance between them

Earth ’ s Gravity The amount of Earth ’ s gravity acting on an orbiting satellite depends on its distance from Earth –The closer to Earth, the stronger the pull of gravity

How is Mass different than weight? Weight –Measure of the force of gravity on an object Not the same as mass Mass is measured in grams or kilograms

Gravity is A Force Gravity is a force and weight is a measure of the force of gravity on an object; therefore, weight is measured in ….Newtons Weight is a measurement of the pull of gravity on a mass

Mass and Weight Mass- The measurement of the amount of matter. Matter- Is anything that takes up space and has mass. “ stuff ”

Mass and Weight Mass is measured with a balance. Weight is measured with a scale –Weight is a FORCE due to gravity. So if gravity is lower, your weight is lower

Practice…. Describe the forces acting on a box that is being pushed to the right along the floor…

Gravity Friction Man pushing Normal force

Normal Force?! Think about it…. Gravity is a downward force on the object- if there wasn’t some upward force to cancel it out, the box would be falling through the floor (net force means object moves) We call this the NORMAL FORCE – the floor exerts the NORMAL FORCE on the box

Applied force Force due to friction Force due to Gravity Normal force

Sir Isaac Newton Isaac Newton used three laws to explain the way objects move. They are often call Newton ’ s Laws. The First Law states that an object that is not being pushed or pulled by some force will stay still, or will keep moving in a straight line at a steady speed. It is easy to understand that a bike will not move unless something pushes or pulls it.

Newton ’ s First Law of Motion – also called the Law of Inertia “ An object at rest stays at rest unless another force acts upon it. An object in motion stays in motion unless another force acts on it. ”

Inertia The tendency of an object to resist a change in motion Demonstrate with paper

Inertia and Mass Rule of Inertia- The greater the mass, the greater the inertia

It is harder to understand that an object will continue to move without help. Think of the bike again. If someone is riding a bike and jumps off before the bike is stopped what happens? The bike continues on until it falls over. The tendency of an object to remain still, or keep moving in a straight line at a steady speed is called inertia.

Another way to think about it The behavior of all objects can be described by saying that Objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force).

Can you think of any everyday examples that shows inertia?

Accelerated Motion Newton ’ s Second Law - is about force and acceleration My Second Law

Newton ’ s 2nd Law of Motion “ A net force acting on an object causes an object to accelerate in the direction of the force applied. ”

2 nd Law Rules The acceleration of the object is affected by two factors: –Size of force – the larger the force acting on the object, the greater the acceleration. –Mass of object- the greater the mass, the greater the force needed to give it the same acceleration.

The Equation Newton ’ s 2nd Law of motion can be expressed with the following equation:  Force = Mass X Acceleration  F = ma

So, why then does….. David Ortiz hit a baseball farther than a 5 year old t- ball player? A soccer ball go further when I kick it than a bowling ball?

Newton ’ s 3 rd Law of Motion

“ For every action there is an equal and opposite reaction. ”

When one object exerts a force on a second object, the second object exerts a force on the first that is equal in size and opposite in direction.

Action Forces and Reaction Forces Forces are always equal in size and are acting on each other. ExampleAction Force Reaction Force See Saw You push down They go up Rocket Propulsion Example?