Forces and Motion Chapter 6 and 7

What is motion? Motion is a change in position. An object changes position if it … moves relative to a reference point.

Reference Point

Distance Distance is the length of the route you travel. Starting Point To find the distance I’ve traveled, I measure my path from my starting point to my ending point. Ending Point

Displacement Displacement is the shortest distance between two points. Starting Point To find displacement measure the difference in position between your starting point and your ending point. ( It also has a direction.) Ending Point

You are a truck driver. If you were getting paid by the mile for your travel, would you rather have your distance or your displacement measured for round trips? Explain….. Distance, it is always greater or equal to the displacement

Speed Speed is how fast something is moving. Speed = Distance divided by Time Try these: What is the average speed of a car that has traveled 300 miles between the hours of 5:00 P.M. and 9:00 P.M.? Drew drove from Wauconda to Crystal Lake in 30 minutes. He traveled a total of 10 miles to his destination. What was his average speed? 75 mph 20 mph

Average Speed Vs. Instantaneous Speed What is the difference between these two types of speed? Give an example….

Were you right? Instantaneous speed is your speed at any given moment in time. Average speed is the average of your speed over a certain distance. When a police officer pulls your dad or mom over for speeding, is he measuring instantaneous speed or average speed? instantaneous

Graphing If you are given the following information, could you graph it? Let’s try….. You need: Title Time(horizontal axis) Distance(vertical axis) Units Spread out your numbers Distance (m) Time (S) 3 7 5 15 30

When did the object stop? It stopped from 5 to15 seconds

Velocity Vs. Speed Speed and velocity measure the same type of motion. What do they have in common? Speed The difference is that velocity also measures… direction. For example, speed is 50 m/s. velocity is 50 m/s north.

Types of Acceleration There are three types of acceleration: Speeding up Slowing down Changing Direction

Calculating Acceleration Acceleration is your change in velocity divided by the time it takes for the change to occur. (final speed – initial speed) time What would be my car’s acceleration if its final speed was 50 miles/hr and its initial speed was 2 miles/hr over 6 seconds? 8 miles/hr-sec

Positive and Negative Acceleration Positive acceleration occurs when you are… speeding up. Negative acceleration occurs when you are … slowing down.

When is the fastest acceleration? The fastest acceleration is between C and D

Mass, Momentum, and Inertia What are they?

Mass Mass is the amount of matter in an object. Which would have more mass, a cotton ball or a lead ball the same size? Lead ball An object that is small may have more mass than an object that is bigger. It just depends on what it is made of.

Momentum Momentum is a measure of how hard it is to stop an object. Momentum is calculated: Mass X Velocity What is the momentum of a car with a mass of 30,000 kg and a velocity of 10 km/hr? 300,000 kgkm/hr

Conservation of Momentum The total momentum of objects that collide with each other is the same before and after the collision. What lab showed this? Marble Lab What happened? The number of marbles at rest or in motion before and after a collision was always the same

Inertia Inertia is the tendency of an object to resist a change in its motion. Inertia is affected by an object’s … mass The more mass and object has, the more difficult it will be to speed it up, slow it down, or turn it because it has more … inertia

Newton’s First Law What is Newton’s First Law? If there is no net force acting on an object, the object remains at rest. If the object is moving, it continues to move in a straight line with constant speed unless acted upon by a force. What are some examples that show this?

Newton’s Second Law What is Newton’s Second Law? Acceleration of an object depends on the force that is applied to an object How does this law relate to sports you know?

Newton’s Third Law What is Newton’s Third Law? For every action, there is an opposite and equal reaction What are some examples of this?

Forces That Act on Objects Gravity: the force that acts between any two objects that have mass Friction: A force that acts to slow down objects in contact with each other Air Resistance: a form of friction that acts to slow down any object moving in the air

What are the three types of friction? Static Rolling Sliding

Types of Friction Static friction: the type of friction that prevents an object from moving when a force is applied Rolling friction: the type of friction that helps a wheel turn and keeps the tire from slipping on the ground Sliding friction: the type of friction that slows down an object that slides What are some examples of each in sports?

Force Force is measured in newtons (N). We use a spring scale to measure newtons. We used these to measure Friction forces Catapult throwing force

Catapults/Trebuchets You need to be able to identify the following parts: throwing arm frame base counterweight axle arm sling projectile cup release angle projectile rubber band Counterweight arm Let’s see what you can do……

Catapult

Trebuchet