General Science Chapter 2 Newton’s 1st Law of Motion Big Idea: A moving object travels in a straight line at a constant speed unless it is acted on by a net force

2.1 Aristotle on Motion Famous philosopher, scientist, and educator in ancient Greece. Made careful observations, collected specimens, and classified all knowledge of the physical world to lay the foundation for Western science. Aristotle taught that natural motion occurred without a force A force is a push or pull Unnatural motion requires forces such as those imposed by people or animals.

2.2 Galileo’s Concept of Inertia In the early 1500’s Italian scientist Galileo demolished Aristotle’s belief that heavy objects fall faster than light objects. - Experiment at Leaning Tower of Pisa - Except for the effects of air friction, objects of different weights fall to the ground at the same time. Galileo stated that a force is required to start an object moving, but once moving, no force is required to keep it moving- except for the force needed to overcome the friction. Inertia= Objects in motion tend to stay in motion. Objects at rest tend to stay at rest. Drop 2 things w diff densities

2.3 Speed and Velocity Speed- the distance covered per unit of time Formula= s= distance/time A person that can run 10 miles in one hour has an average speed of 10m/hr Instantaneous Speed- Speed at any given instant. Velocity- Speed AND direction of an object …What’s the difference between speed and velocity? Vector quantity-a quantity that specifies direction as well as magnitude.

Speed Problems What is the average speed of a cheetah that sprints 100m in 4s? What if it sprints 50m in 2s? Wonder Woman speeds around a 1320-m long racetrack in 2 minutes. Calculate her average speed in m/min. Also calculate her speed in m/s. Chef Pinkerton can decorate flowers on 300 cupcakes in half an hour. How many cupcakes can he make in an hour? Betsy wrapped 5 presents in 15 minutes. If she continues at this rate, how many presents will be wrapped in one hour?

2.4 Motion is Relative Everything is always moving. We are currently speeding through space. When discussing how any object moves, we mean its motion relative to something else. A car that reaches 120 miles an hour is relative to the road. We are moving at 100,000 km/hr, relative to the Sun

2.5 Newton’s First Law of Motion-The Law of Inertia Isaac Newton’s laws were based off of Galileo’s findings Newton’s 1st Law: Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force -The law also states that when an object is moving, it tends to remain moving, along a straight-line path. …In other words: An object at rest tends to stay at rest unless acted on by a force, and an object in motion tends to stay in motion unless acted on by a force.

2.6 Net Force- The Sum of All Forces on an Object -It is the net force that changes an object’s state of motion. Newton- The scientific unit of force. Abbreviated as “N” Forces are indicated by arrows in illustrations. Arrows are used because forces are vector quantities.

2.7 Equilibrium for Objects at Rest When you put a fruit in the hanging scale at the supermarket a spring in the scale stretches until it reads the weight. This stretching force is called tension. Both pounds and Newtons are units of weight. Units of weight are also units of force. 2 forces act on an object. Tension force- acting upward. And weight (or gravity) acting downward. When the net force on an object is zero, its state of motion doesn’t change, and we say that the object is in mechanical Equilibrium. Equilibrium rule=

2.8 The Support Force- Why We Don’t Fall Through the Floor An object that is not moving, such as a book has a net force of zero. One of the forces acting on the book is gravity. Support force- The upward force The support force plus gravity add mathematically to become zero. So the net force on the book is zero. ∑F=0 What is the net force on a bathroom scale when a 100-lb person stands on it? If that same person stood evenly on 2 scales what would each scale read? What would happen if they stood unevenly on the scales? 0N

2.9 Equilibrium for Moving Objects An object at rest is in equilibrium. An object is also in equilibrium if it moves steadily, without changing its state of motion. The sum of all forces will still equal 0 Before the 16th century people believed that Earth was at the center of the universe. Bird dropping to catch worm argument When the bird drops from the branch, its initial sideways motion remains unchanged. It catches the worm quite unaffected by the motion of its total environment -Must consider relativity. Bird is moving through space at the same rate that its environment is.