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 in Newtons with a spring scale. 1 kg accelerated at 1 m/s2 would require 1 N of

force. A small apple weighs about 1 Newton.

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-upAre forces scalar or vectors?

Thumbs up – ScalarThumbs 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.

Fg Fn Fg

Fn 50N, up

50N, down

If forces are unbalanced…Motion• Net (unbalanced)

force.

Fg

FnFn

Net force

Fg

Direction of motion

Friction Friction force is a force that resists or opposes motion. Friction force is present when other forces are present. Types of Friction

Static FrictionActs 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?

StaticSlidingRollingFluid

Where does gravity act?Everywhere even in space