Newton’s Laws

But First… * STORY TIME ABOUT ISAAC NEWTON

Please CORRECT ON YOUR ENGINEERING NOTES Problem: Build a vehicle that moves forward by pushing backwards (Newton’s 3 rd Law) & accounts for Newton’s 1 st & 2 nd Laws Parameters: Must travel 1.5 meters forward using Newton’s 3 rd law

Newtons 1 st law What does Newton’s First Law (The Law of Inertia) state? An object at rest will remain at rest, and an object in motion will continue in motion at a constant velocity unless acted upon by a outside force.

What is inertia?Inertia is the resistance to change in motion. The greater the mass, the greater the inertia

Demonstration EGG MAN IN THE CAR GOING DOWN A RAMP

Lets try the table cloth trick Try using coins of different mass. Try using an empty cup vs. cup with a little water in it.

What are some outside forces that might act on an object Wall, Brakes Surface Friction GravityAir Resistance

Newton’s First Law can be used to explain why the planets stay in orbit

What is Newton’s Second Law of Motion? Example 1: You would be able to accelerate a wagon pulling a certain mass more than your baby brother/sister because you could apply a greater force. The net force on an object is equal to the product of its acceleration and mass. Example 2: As the mass of what is in the wagon decreases, the same force will cause a greater acceleration. Force (N) = Mass x Acceleration

Everyone knows that heavier objects require more force to move the same distance as lighter objects. More mass means more force needed to accelerate. Ouch!Fun!

How can you increase acceleration? You can increase acceleration by increasing the force; decreasing the mass; or both. F= M X A

Sample Problem Answer this on the same page as your foldable. Show your work! Solve: A 52 kg Water-skier is being pulled by a speedboat. The force causes her to accelerate at 2m/s2. Calculate the net force that causes the acceleration. Force = Mass X Acceleration Force = 52kg X 2m/s2 Force= 104kg X m/s2 Force= 104 N

Related Term: MOMENTUM A measure of how hard it is to stop an object. Objects will have greater “momentum” if they have a larger mass or velocity. A bullet has a large momentum even though its mass is small because it has a high velocity. A baseball moving at 20m/s has less momentum than a car moving at 20m/s because it has less mass. Momentum=Mass X Velocity (kg  m/s)

Sample Problem: Which has more momentum: a 3 kg sledgehammer swung at 1.5m/s or an 4 kg sledgehammer swung at.9m/s? Momentum = Mass x Velocity Lighter sledgehammer: 3 kg X 1.5 m/s = 4.5 kg*m/s Heavier sledgehammer: 4kg X.9 m/s = 3.6 kg*m/s Answer: The lighter hammer has more momentum because it is swung at a greater velocity—almost twice as fast.

What is the law of conservation of momentum? The total momentum of any group of objects is the same before and after they interact unless acted on by an outside force. Newton’s Cradle

What is Newton’s Third Law of Motion? For every action, there is an equal (in size) and opposite (in direction) reaction.

What are some examples of Newton’s 3rd law in nature? 2) A Squid Swimming Action Force: A squid pushes water back when swimming Reaction Force: The expelled water pushes forward with an equal force and forces the squid to move ahead. 3) A Hammer And A Nail Action Force: A hammer pushes a nail down into the wood. Reaction Force: The nail pushes back up on the hammer causing it to come to a suddenly stop. 1) A Bird Flying Action Force: The bird pushes the air downward with its wings. Reaction Force: The air pushes back on those wings with an equal force that propels the bird upward.

While driving down the road, an unfortunate bug strikes the windshield of a bus. This is a case of Newton's third law of motion. The bug hit the bus and the windshield hit the bug. Which of the two forces is greater: the force on the bug or the force on the bus? Trick Question! Each force is the same size. For every action, there is an equal... (equal!) and opposite reaction. The fact that the bug splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction.

What is the equation for momentum?