Chapter 11 Section 2 Forces and Motion

What are Forces? Force - is a push or pull that causes an object to move faster or slower, stop, change direction, or change size or shape. Objects do not need to be touching in order for a force to occur Without force, nothing would ever move.

Gravity- the force that attracts all objects together. *The greater the mass, the greater the pull!!! *The greater the distance the weaker the pull!! Discovered by Sir Isaac Newton when an apple fell upon his head… Gravity

Friction Friction is a force that opposes the motion of one object moving past another. Friction is affected by the surfaces of the two objects and how hard they are pressed together. *It is always present when two surfaces rub together. Would objects with bumpy or smooth surfaces have more friction when rubbed together?

Examples of Friction Friction keeps us from sliding off the skateboard. The rough surface of the mountain causes friction and gives us a grip on the side of the mountain when we rock climb. T he tread on our shoes causes friction, and keeps us from ending up like this guy on icy roads.

Air Resistance Air Resistance- air hits a moving object and slows it down Air resistance increases with velocity *Water can also slow objects down If there was no air resistance which object would hit the ground first a feather or a bowling ball?

Balanced forces are equal in size and opposite in direction. When forces are balanced, no change in motion occurs. Balanced Forces

Unbalanced forces are NOT equal in size and opposite in direction. When forces are unbalanced, a change in motion occurs. Unbalanced Forces

Newton’s First Law of Motion An object at rest tends to stay at rest and an object in constant motion tends to stay in motion, unless acted upon by an unbalanced force. Inertia- the tendency of an object to move in a straight line Newton’s first law is also known as ?

Newton’s 1 st Law and You *Because of inertia, objects resist changes in motion. When the car is going forward and is stopped by the brick wall, your body wants to keep moving forward at the speed the car was traveling. *Don’t let this be you. ! *Don’t let this be you. Wear seat belts !

Newton’s Second Law of Motion The unbalanced force of an object is equal to the mass of the object multiplied by its acceleration. Force= Mass x Acceleration The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). Force is measured in Newtons (N) How much force would I need to move a 20 lb wheelbarrow at (5m/s) ?

Newton’s Third Law of Motion All forces occur in pairs, and these two forces are equal in strength and opposite in direction. More commonly know as “For every action there is an equal and opposite reaction” Action force- the push of the first object on the second Reaction force- the push of the second object back on the first

Examples of Newton’s Third Law The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

Chapter 11 Section 2 Review! Rules All responses need to be in question form. Questions answered wrong will result in negative points. Its Time for Jeopardy !!!!!!!!!!!!!!!!!!!!!!