Transcript Slide 1
Have you ever stopped to look at a car accident? When you look at a car accident you are looking at the results of the Forces of Motion around us. Newton’s Laws of Motion REVIEW First we need to define the word FORCE: • The cause of motion (what causes objects to move) • Two types of forces – Pushes – Pulls REVIEW Forces are measured in Newtons • SI unit of force • Symbol: N • Measured by using a spring scale REVIEW Forces may be balanced or unbalanced • Balanced forces – all forces acting on an object are equal – There is NO MOTION • Unbalanced forces – one or more forces acting on an object are stronger than others – There is MOTION • A NET FORCE Newton’s Laws • First Law – Inertia • Second Law – Acceleration, Force & Mass • Third Law – Action-Reaction Law # 1: Every object at rest remains at rest and every object in motion continues moving in a straight line at a steady rate unless a force acts it on. This is the principle of inertia. Can you tell me how this principle applies to car accidents? First Law • Inertia & Mass – Mass is the amount of matter in an object. – The more MASS an object has, the more INERTIA the object has. – Bigger objects are harder to start & stop. http://toons.artie.com Law # 2 The amount of force needed to change the speed of an object depends on the mass of the object and the amount of acceleration (or deceleration) needed. This is the principle of accelerated motion. Can you tell me how this law applies to car accidents? Second Law • Acceleration & Force – The more force placed on an object, the more it will accelerate [change its motion]. • Acceleration & Mass – The more mass [or inertia] an object has, the more force it takes to accelerate the object. Second Law Force = Mass x Acceleration Example: A 25 g object with an acceleration of 4 m/s2 will have a force of ______ Newtons. Law # 3 For every action there is an equal and opposite reaction. When an object is pushed or pulled by a force in one direction, another force pushes or pulls on it with equal strength from the opposite direction. Forces come in pairs, called action-reaction pairs. How does this law apply to car accidents? Third Law • Action – Reaction – Forces are always produced in pairs with opposite directions & equal strengths. – For every force there is an equal and opposite force. Third Law • Action – Reaction – Action – Reaction Forces act on different objects… • When you kick a soccer ball, you exert a force on the ball and the ball exerts a force on you. The harder you kick the bigger the force on you (kicking REALLY hard might hurt.) Third Law Which Law? A swimmer pushes water back with her arms, but her body moves forward. Which Law? A frog leaping upward off his lily pad is pulled downward by gravity and lands on another lily pad instead of continuing on in a straight line. Which Law? After you start up your motorcycle, as you give it more gas, it goes faster. Which Law? A pitched baseball goes faster than one that is gently thrown. Which Law? When you paddle a canoe, the canoe goes forward. Which Law? As an ice skater pushes harder with his leg muscles, he begins to move faster. Which Law? A little girl who has been pulling a sled behind her in the snow is crying because When she stopped to tie her hat on, the sled kept moving and hit her in the back of her legs. All about Forces! A. B. C. D.