1. Motion What causes an object to start moving, stop moving, or change direction???

2. Forces Force- a push or a pull that makes an object move -can measure forces to see how big or small -measured in Newton’s (N) What are some examples of forces???

3. Forces There are three types of forces: 1. Balanced forces- the object does not change motion 2. Unbalanced forces- will cause an object to start moving, stop moving, or change direction (the object will move in the direction of the greatest force) 3. Net force- a combination of all forces acting on an object (adding all forces together)

4. Balanced or unbalanced? 1. pushing a desk across a room 2. pushing against a brick wall 3. Playing tug of war 4. two students pushing against opposite sides of a door 5. pushing someone down a hill on a sled

5. Forces Friction- a force that opposes motion between two surfaces that are in contact Any examples of friction??? Rubbing hands together to stay warm Brushing your hair Pushing a box that is moving Starting a fire with two sticks

6. Friction Do rough surfaces or smooth surfaces create more friction? Surfaces will push together more when they are rough The rough spots on a surface get stuck on the rough spots of the other surface

7. Friction 3 types of friction 1. sliding friction- when an object slides over a surface (Any examples?) 2. rolling friction- when an object rolls over a surface (Any examples?) 3. fluid friction- when an object moves through a fluid (Any examples?)