Unit 01 “Forces and the Laws of Motion” Test Review

What Do I Need To Know? Content Constructed Responses Lab Skills Net Force, equilibrium, force diagrams, Newton’s Laws Constructed Responses Identify which Law and answer questions with A.E.S. Lab Skills No graphing this time … because we need to practice this skill first! Problem Solving FNet=F1+F2+F3+… F=ma Fw=mg

Force A force is a Push or a Pull Net force: All forces on an object. A NET force can change the motion of an object. Net force: All forces on an object. Unit: Netwons (N)  Kgm/s2

There are 3 ways a Net Force can affect the motion of an object. A Net Force ACCELERATES an object… which means it can make an object… Speed Up Slow Down Change Direction

Force Diagram or Free-Body Diagram Different size arrows – Accelerating! Speed up, slow down or change direction! A picture of the forces on an object. Box represents object. Arrows represent forces. Different sizes to show different amounts of force A cow has two forces on it… 34N East, 50N West F= 50N F= 34N Force Diagram

Same size arrows – Equilibrium- F = 68 N F = 68 N Same size arrows – Equilibrium- Constant Velocity Or At Rest! Equilibrium The forces on an object add to zero. Fnet = 0 The forces on the object are “balanced” An object in equilibrium can: Not move (motionless) Move with a constant velocity

Define Force, Net Force and Equilibrium. List 3 ways a Net Force can change motion: Which force diagram shows an object in equilibrium? An object in Equilibrium can have 2 motions: What is the net force on a box moving with a constant velocity of 60m/s? Draw a force diagram for a book pushed forward at a constant velocity in the presence of friction for a book accelerating forward in the presence of friction.

Push or a Pull The sum of all the forces on an object. Define Force: Define Net Force: Define Equilibrium: Push or a Pull The sum of all the forces on an object. The forces on the object add to zero. FNet=0 The forces on the object are balanced.

Speed Up Slow Down Change Direction FNet = 0 List 3 ways a Net Force can change motion: 3. Which force diagram shows an object in equilibrium? 4. An object in Equilibrium can have 2 types of motion: Speed Up Slow Down Change Direction Motionless (not moving) Moving with a Constant Velocity (not speeding up, not slowing down, not changing direction) 5. What is the net force on a box moving with a constant velocity of 60m/s? constant velocity FNet = 0

6. FN (Normal Force) FN (Normal Force) Fpush Fpush Ffriction Ffriction Fw (gravity) Fw (gravity) Different sized arrows show NET FORCE – accelerating! Same sized arrows show EQUILIBRIUM– at rest or constant velocity!

What is Newton’s 1st Law of Motion What is Newton’s 1st Law of Motion? List at least one example of the 1st Law shown in class. What is Newton’s 2nd Law of Motion? List at least one example of the 2ndLaw shown in class. What is Newton’s 3rd Law of Motion? List at least one example of the 3rd Law shown in class. What happens when a cart with a big mass and a cart with a small mass are pushed with the same force? Which Law does this demonstrate? What happens to a person without a seatbelt who is in a moving car if the car suddenly stops? Which Law does this demonstrate? What happens when a balloon filled with air is released? Which Law does this demonstrate?

“Inertia” “An object at rest will stay at rest and 1. What is Newton’s 1st Law of Motion? List at least one example of the 1st Law shown in class. “Inertia” “An object at rest will stay at rest and An object in constant velocity motion will stay in constant velocity motion Unless acted on by an unbalanced force.” Examples: Tablecloth trick Hoop/Nuts Boy on Skateboard Guy on Bus Car Accidents (Seatbelts) Ball in Truck

F=ma “The acceleration of an object is 2. What is Newton’s 2nd Law of Motion ? List at least one example of the 2nd Law shown in class. F=ma “The acceleration of an object is directly proportional to the force applied to object. The acceleration of an object is inversely proportional to the object’s mass” Examples: Skateboarders Basketball and Tennis Ball Heavy and Light Carts Earth and Object

3. What is Newton’s 3rd Law of Motion 3. What is Newton’s 3rd Law of Motion? List at least one example of the 3rd Law shown in class. Action/Reaction “For every force applied to an object, the object applies an equal and opposite force back.” Examples: Balloon Rocket Walking “Pushing off table” Newton’s Cradle Punching A Face

4. What happens when a cart with a big mass and a cart with a small mass are pushed with the same force? The objects pushed off each other With equal and opposite forces And both moved back, the one with less mass faster. The cart with more mass accelerates less, the cart with less mass accelerates more! Newton’s 2nd Law states: acceleration and mass are inversely proportional More mass, less acceleration. Less mass, more acceleration.

5. What happens if a person is moving in a car and then the car suddenly stops? When the car suddenly stops the person continues moving. According to Newton’s 1st Law an object in motion will stay in motion unless an outside force is applied. There was a force on the car, so the car stops. But there is no force on the person, so they continued moving.

6. What happens when a balloon filled with air is released? When released… The balloon moved forward And the air moved backwards. The balloon pushed the air out (action) So the air pushed the balloon too (reaction) Newton’s 3rd Law states: for every force put on an object [the action], that objects puts an equal and opposite force back [the reaction].

Action-Reaction Pairs The air molecules push the flag. The Earth pulls a ball down. I push the chair forward. The chair pushes me backwards. The flag pushes the air molecules The ball pulls the Earth up. With equal and opposite force!!!!

A. E. S. Look at the data table below A.E.S. Look at the data table below. What factor affects the acceleration of an object? Object Force (F) N Mass (m) kg Acceleration (a) m/s2 Round Ball 100 50 2 Box 15 7 Rubber Ducky 4 25

Look at the data table below Look at the data table below. What factor affects the acceleration of an object? The mass of the object affects it’s acceleration. According to Newton’s 2nd Law mass and acceleration are inversely proportional. The object with greater mass of 50kg had the smallest acceleration of 2m/s2. While the object with the smallest mass of 4kg had the greatest acceleration 25m/s2.

A.E.S. A girl at a roller rink was trying to skate so she “pushed herself off the table” to begin moving backwards. Why is it wrong to say “she pushed herself off the table”?

A girl at a roller rink was trying to skate so she “pushed herself off the table” to begin moving backwards. Why is it wrong to say “she pushed herself off the table”? It is wrong to say “she pushed herself off the table” because she pushed the table, not herself. According to Newton’s 3rd Law, for every force applied to an object the object applies an equal and opposite force back. In this case the girl pushed the table and the table pushed her back. This is why she moved.

A. E. S. A truck is driving with passengers in the bed of the truck A.E.S. A truck is driving with passengers in the bed of the truck. When the truck stops quickly do the people “fly out” because they get pushed forward?

A truck is driving with passengers in the bed of the truck A truck is driving with passengers in the bed of the truck. When the truck stops quickly do the people “fly out” because they get pushed forward? No, the people do not get pushed forward. According to Newton’s 1st law, an object in constant velocity motion will stay in constant velocity motion unless acted on by an outside force. The truck and the people were moving but only the truck had a force on it, so it stopped. There was no force on the people so they CONTINUED to move forward … they were not pushed forward.

Write the Equations for… Net Force Force Weight Fnet = F1+F2+ … F = ma Fw= mg

What is the weight of a 60kg woman on Earth? Complete the following problems in your groups using the 5-Problem Solving Steps What is the weight of a 60kg woman on Earth? What is the net force on a box which has a mass of 20kg and an acceleration of 5m/s2. Find the net force on a rope if it is pulled to the right with a force of 75N, pulled to the left with a force of 55N and left with a force of 30N. What is the acceleration of a 200kg car pushed with a force of 600N? What is the mass of a toy car if it is pushed forward with a force of 78N forward and friction applies a backwards force of 18N resulting in an acceleration of 2m/s2? Answer: 588N Answer: 100N Answer: -10N Answer: 3m/s2 Answer: 30kg

Solve using the Problem Solving Steps. What is the weight of a 60kg woman on Earth? Fw = mg Fw = (60kg)(9.8m/s2) Fw = 588 kgm/s2 Fw = 588N Fw = ? m = 60kg g = 9.8m/s2

F = ma F = (20kg) x ( 5m/s2) F = 100 kgm/s2 F = 100 N Solve the problem using the “Problem Solving Steps”. What is the net force on a box which has a mass of 20kg and an acceleration of 5m/s2. F = ma F = (20kg) x ( 5m/s2) F = 100 kgm/s2 F = 100 N F = ? m = 20kg a = 5m/s2

Solve using the Problem Solving Steps. Find the net force on a rope if it is pulled to the right with a force of 75N, pulled to the left with a force of 55N and left with a force of 30N. FNet=F1+F2+ F3 FNet= 75N + (-55N) + (-30N) FNet= 75N + (-85N) FNet= -10N Fnet = ? F1 = 75N F2 = -55N F3 = -30N

Solving using the Problem Solving Steps. What is the acceleration of a 200kg car pushed with a force of 600N? a = ? m = 200kg F = 600N F = ma 600 N = (200kg) x (a) 600 kgm/s2 = (200 kg)(a) 200kg 200kg 3m/s2 = a

Solve using the Problem Solving Steps. What is the acceleration of a 30kg toy car if it is pushed forward with a force of 78N forward and friction applies a backwards force of 18N? FNet=F1+F2 FNet= 78N + (-18N) FNet= 60N Fnet = ? F1 = 78N F2 = -18N F = ma 60 N = (30kg) x (a) 60 kgm/s2 = (30kg)(a) 30kg 30kg 2m/s2 = a a = ? m = 30kg