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# 7-1 Forces

## on Dec 14, 2009

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## 7-1 ForcesPresentation Transcript

• Warm-Up
Which encounters a greater force of air resistance? A feather or an elephant. Explain.
There is greater force of air on the elephant because its surface area is large. But the force of air on it is very small compared to its weight.
• 7-1 - Forces
Describe examples of force and Identify appropriate SI units used to measure force.
Explain how motion of an object is affected when balanced and unbalanced forces act on object.
Compare and Contrast the four kinds of friction.
Describe how Earth’s gravity and air resistance affect falling objects.
• Force
A push or a pull that causes a change in motion.
Measured inNewtonswith a spring scale.
1 kg accelerated at 1 m/s2 would require 1 N of force.
A small apple weighs about 1Newton.
• Forces that affect motion
Fa- Applied Force
a force exerted on an object by other objects in it’s environment.
Ff - Frictional Force
a force that opposes motion between the object and the surface it rests upon.
Fg- Gravitational Force
the force of attraction between two objects with mass.
(ex. Between an object and the Earth)
Fn - Normal Force
the supportive force of the surface an object rests upon.
Normal means “perpendicular”
Fnet –Net Force
Sum of all forces
• Understanding Check-up
Are forces scalar or vectors?
Thumbs up – Scalar
Thumbs down – vector.
Does the direction of the push matter?
• Combining forces acting on an object
• Force Diagrams
Arrows drawn to represent the size and direction of force.
All arrows are drawn from center of object.
• If forces are balanced…No Change Motion
• No net (unbalance) forces.
Fn
50N, up
Fg
Fn
Fg
50N, down
• Direction of motion
If forces are unbalanced…Motion
• Net (unbalanced) force.
Net force
Fg
Fn
Fn
Fg
• If forces are balanced…No Change in Motion
No net (unbalance) forces.
Ff
Fn
Ff
Fn
Fg
Fg
• Friction
Friction force is a force that resists or opposes motion.
Friction force is present when other forces are present.
Types of Friction
Static Friction
Acts on objects that are not moving but other forces are trying to move the object .
Sliding Friction
Acts on object that is moving.
Rolling Friction
Acts on objects that roll.
Fluid Friction
Acts on objects that are in fluids.
A fluid is matter that can flow and has no shape.
• Gravity
Gravity is an attractive force that acts between two masses.
Gravity acts towards the center of the earth or any other object.
Gravity’s affects are everywhere.
There is gravity in space. Its just very small.
• Summary of Forces
What is a force?
A push or a pull that causes acceleration.
What are the four type of friction?
Static
Sliding
Rolling
Fluid
Where does gravity act?
Everywhere even in space