Forces are pushes or pulls that cause changes in motion or acceleration. There are four main types of friction: static, sliding, rolling, and fluid friction. Gravity acts everywhere, pulling objects toward the center of masses like the Earth. Gravity affects falling objects, along with air resistance from the atmosphere. Balanced forces cause no changes in motion, while unbalanced forces result in movement.

1. 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.

2. 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.

4. 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.

5. 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

6. Understanding Check-up Are forces scalar or vectors? Thumbs up – Scalar Thumbs down – vector. Does the direction of the push matter?

7. Combining forces acting on an object

8. Force Diagrams Arrows drawn to represent the size and direction of force. All arrows are drawn from center of object.

11. If forces are balanced…No Change in Motion No net (unbalance) forces. Ff Fn Ff Fn Fg Fg

12. 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.

13. 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.

14. 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