Aim: How can we apply Newton’s 1st and 2nd Law? Do Now: Quiz HW: Problem Set

Newton’s First Law 1. How does this describe Newton’s First law?

An object at rest will stay at rest until acted on by an outside force 1st Law: Every object continues in it’s state of rest or of uniform velocity in a straight line as long as no net force acts on it. What happens to you when you are in a car and it comes to a complete stop? How does a seat belt help you? An object at rest will stay at rest until acted on by an outside force An object in motion will stay in motion until acted on by an outside force This is called inertia

MORE MASS means MORE INERTIA Also known as the law of Inertia Inertia is an objects tendency t to stay in motion. LOTS OF INERTIA hard to… GET MOVING or STOP MORE MASS means MORE INERTIA

If pushed with an equal force, which toy car will cross the finish line first? Explain. Newton’s Second Law of Motion (F= m a) An object with more mass requires more force to accelerate An object with less mass requires less force to accelerate.

Newton’s Second Law “The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the mass of the object.” Sum of forces is an important concept because it can help us solve for an objects acceleration!

With a Partner, label all the forces with a free body diagram. Assume the block is moving at a constant speed against friction. What does this mean? ΣF = 0, no acceleration Use the 4 Step Method!

Force to Stop a Car What average net force is required to bring a 1500 kg car to rest from speed of 100 km/hr within a distance of 55m? We can use Newton’s 2nd law if we know the mass and acceleration!

Station Activity Explain in full sentences the situation described. Then support that statement with an expression.

Using a Spring Scale and a mass, pull at a constant speed. Describe the forces acting on the block in terms of newton’s second law. Write an expression showing the block in equilibrium.

Using a Spring Scale and a mass, pull the block with an increasing velocity. Describe the forces acting on the block in terms of newton’s second law. Write an expression showing that the block is acted on by an unbalanced force.

Buoyant Force From the name alone, what kind of force are we dealing with? This force acts upwards in a liquid. Archimedes Principle: The buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object.

Buoyant Force Demo Using a force probe, I will measure the weight of my mass. …I have a mass on a string. What will my FBD look like? How will the tension be affected by the buoyant force?

FBD T T FB W W More pressure ≠ More force pushing up Pressure pushing up or force of fluid is the same despite depth.

Summary When does an object start to accelerate? What is Newton’s First Law? For an object in motion, what causes it to stop normally? How does this involve the second law? Provides additional upward force which lowers the tension. Buoyant force is cut in half.