Forces and Newton’s Laws of Motion Newton’s 1st Law If an object is under the influence of force, does it have to have a displacement? Why or Why not?

Forces and Newton’s Laws of Motion Newton’s First Law

Objectives What are Newton’s 1st Law, inertia, and equilibrium? How are mass and inertia related? What is net force and how does it determine equilibrium?

Newton’s 1st Law of Motion “An object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an unbalanced net force.” Also known as the Law of Inertia I N E R T I A

Inertia Inertia is the tendency of an object to resist a change in its motion. Mass is a measure of inertia. More mass = more inertia Killer tissue box

Newton’s 1st Law of Motion “An object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an unbalanced net force.” What do you think is an “unbalanced net force?”

Net Force (∑F) “the sum of” The vector sum of all forces acting on an object. “Vector” means direction is important If the vector sum of the forces is not zero then there is a net force. ∑F ≠ 0, The forces are unbalanced and motion will change. Changing velocity If the vector sum of the forces is zero then there is no net force. ∑F = 0, The forces are balanced and the motion won’t change. Constant velocity

Equilibrium Balanced forces and a net force of zero describes a state of equilibrium. Equilibrium: the state in which there is no change in an object’s motion. The sum of all forces equals zero. FN Fg ΣFy = FN + Fg = 0 ΣFx =

Net Force Balanced on the y-axis Balanced on the y-axis Balanced on the x-axis Unbalanced on the x-axis Equilibrium Not Equilibrium Balanced Forces… No Net Force (∑F = 0) Constant Velocity Unbalanced Forces… Net Force (∑F ≠ 0) What happens? *Cart will Accelerate to the right

Calculating Net Force Quick Reminder: An 8 kg monkey is hanging from a vine. What is the tension in the vine? A 21kg kid is sitting in a swing supported by two cables. What is the tension in each cable? Two children pull on a stuck toy with a force of 12N at angles of 30º. If the object is in equilibrium (the toy does not move) how much force is resisting the children? An art piece is hanging in a museum as shown. What is the tension in each chain holding it up if the piece of art has a mass of 20 kg? Quick Reminder: Weight is the force on an object due to gravity. Weight = mass x gravity Fg = mg Quick Reminder: When you see a vector at an angle you break it into it’s components. 12N 30o Fancy Art 30o

S.T.A.M.P. Curators hang a piece of art from the ceiling in a museum. The cables are at angles as shown. What is the tension in each cable assuming the art has a mass of 500 kg? 67° 180° Regular T1= 5331.5 N T2= 2084 N

Practice A 500 kg container is held in the air by two cables like the picture shown. What is the tension in each cable? 60o 15o Honors

S.T.A.M.P. A 910 kg car passes through the middle of a bridge. What force must the support beams be able to handle? (Ignore the mass of the bridge) Honors 55o 30o

Exit Ticket If an object is under the influence of force, does it have to have a displacement? Why or why not? Has your answer changed since the lesson?