Goal 4 - Gravity and Newton’s First Law Show the box and balloon as described in the plan accompanying the PPT Lead the discussion to find out how much they already know- this will vary across the class. During activity 2: As they try the different examples of forces acting, ask them what is happening as the forces act. Is gravity real - or does the Earth just suck?

THE HISTORY OF GRAVITY Sir Isaac Newton wrote the Law of Gravitation in 1687

Gravity is a force When gravity pulls something towards the Earth - - we call this force the weight (a measure of gravity). We can understand that Gravity is a force because it makes things move Hold an object on your hand What is stopping it moving? You can feel the downward force on it pushing on your hand

Law of Gravity The size of the force depends on the mass of the objects. The bigger they are, the bigger the force! Small attractive force Bigger attractive force

Law of Gravity More Less The size of the force also depends on the distance between the objects. More Less

ping pong ball falling The arrow represents the force of gravity This slide shows the force on the ping pong ball when dropped.

The ball does not fall when your Normal = force of gravity table Normal (upward force) gravity They will find it very difficult to pass the ball around because the force to lift the ball must be upwards to balance the force of gravity.

two objects dropped at the same time Explain that the two objects are released at the same time. As they fall the light flashes at a steady rate. For each flash the positions of the objects are shown at the same moment The pictures show that the ping pong ball and the marble fall at almost the same rate. The marble actually reaches the ground first. Explain that this is because there is air resistance slowing the larger object down (more than the small object).

On the Moon – Apollo 15 A heavy geological hammer and a falcon feather were dropped from the same height. They hit the lunar surface at the same time. If possible show them a video of the experiment when the astronaut David Scott dropped a hammer and a falcon feather on the Moon. Explain that there is no air (atmosphere) on the Moon so both the hammer and the feather reach the surface at the same instant- if released at the same instant. NASA pictures

Problems You measure a bag of apples as weighing 85 N on a scale. How massive is the bag of apples? Given: Weight= 85 N Gravity = 9.8 N/kg m = 8.67 kg m = 85N/9.8 N/KG

Newton's First law

Newton's First law An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force.

Try this at home!

Unbalanced vs. balanced force Can cause an object to start moving, stop moving or changes direction. Result in a net force and cause a change in the object's motion. Balanced Do not change the object's motion. Equal force in opposite directions.

At rest Object not moving WILL NOT move unless an unbalanced force acts on it. Homework will not get done on it's own. Your room will not be cleaned on it's own.

In Motion Object in motion (velocity) will stay in motion.   Object in motion (velocity) will stay in motion. Outside force can change it's speed, velocity, or direction.

What makes things slow down on their own? Friction Gravity

Inertia Concept of resistance to change in motion. Tendancy of an object to resist that change in motion. Newton's First Law - Law of Intertia

Inertia Depends on Mass Some objects have more Inertia than others. Empty aquarium vs. Full Aquarium The greater the mass of an object, the greater it's Inertia, the greater the force required to change it's motion.

Inertia Depends on Mass

Newton's Law of Inertia

Students will be able to explain Newton's first law. Goal 4 Students will be able to explain Newton's first law.