Warm Up What is net force? What is true about net force when all the forces acting on an object are balanced? What does this mean for the motion of the object? What is true about net force when all the forces acting on an object are unbalanced? What is friction? How do you know that friction must be a force? What is gravity? How do you know that gravity must be a force? What is normal force? Does an object hanging in the air have normal force?

Think, Pair, Share Why do things move? If you are riding in the car with your seatbelt on, what does your body do when the driver hits the brakes suddenly? Why? If a puck is sitting on the ice in a hockey game, does it start moving on its own? 30 s to think, 2 min to talk, call on 1 group to share (REPEAT DIRECTIONS BEFORE STARTING)

Physics and the NFL http://nbclearn.com/nfl

What is Newton’s First Law of Motion? An object at rest remains at rest, and an object in motion continues in motion with constant velocity in a straight line, unless acted upon by an unbalanced force Objects are going to keep doing what they’re doing

Newton’s First Law of Motion Also known as the “Law of Inertia” Inertia: tendency of an object to stay in its state of motion It is not in an object’s nature to start moving if it is stopped or stop moving once it is set in motion In the absence of a net external force, a body will preserve its state of motion In other words, on object will keep doing what it’s doing Inertia = “laziness” It is not in an object’s nature to stop once it is set in motion. Rather, it is an object’s nature to maintain its state of motion.

How does mass effect inertia? The greater the mass of an object, the greater the net force required to get it moving or to change its motion Therefore, the greater the mass, the greater the inertia Which has the most inertia?

Newton’s First Law of Motion Imagine that hockey puck on the ice. Unless it is hit by a stick, it will sit on the ice indefinitely If it has been hit by a hockey stick—if there were no friction, air resistance, and the ice was infinitely large, the puck would continue to move without any change in velocity Air resistance is friction in the air No change in velocity – what is acceleration?

Newton’s First Law and You What is the force acting here? Is it balanced or unbalanced? Is there acceleration? Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hr is stopped by the brick wall, your body keeps moving at 80 km/hr.

Newton’s First Law of Motion Is there an unbalanced force acting on this golf ball? No. What is the golf ball’s acceleration? What needs to happen in order for the golf ball to gain an acceleration? An unbalanced force needs to act on it.

Newton’s First Law of Motion Once airborne, will the golf ball ever stop? On Earth, yes. What is the unbalanced force that acts on the golf ball in the air? Air resistance (friction in the air)

Mass vs Weight Mass – amount of matter in an object (kg) Weight – the force of gravity on that mass (N) W = mg