Physical Science Mr. Barry

F=ma  As you’ve learned from Newton’s 2 nd Law, Force can be found by multiplying mass and acceleration  Reactionary Forces  Newton’s 3 rd Law: “For every action there is an equal and opposite reaction”  This applies to forces such as gravity and force generated by movement as well

Reaction to Movement  There is a reactionary force to movement know as friction  Friction: the force that opposes motion between two surfaces that are touching each other  Depends on the types of surfaces rubbing against each other and the types of forces causing movement

Friction  Low friction = easy to slide on (ice, oil)  High friction = hard to slide on (sandpaper, gravel)  If the friction force is greater than or equal to the force of movement, not movement will occur  What type is happening on the right?

Friction on Force Diagrams ALWAYS opposes motion (acts in opposite direction)

Reaction to Gravity  Look at your notebook sitting on your desk right now. If gravity is pulling it down, what is keeping it from falling to the floor?  The force that opposes gravity is known at the Normal Force  The normal force will always be equal to the force of gravity (as long as no other forces are acting in the vertical direction)  The normal force will always be opposite the direction of the force of gravity (UP)

Normal Force  The heavier the object, the greater the gravitational force and thus the greater the normal force  If the mass of the object on the left is 6 kg, what is the normal force acting on it?  If the object is resting on a table, what is providing the normal force?

Normal Force on Force Diagrams