Motion Force Unit 1 Grade 8

Motion & Force Unit 1

Grade 8 Science Standards • S 8 P 3 Students will investigate relationships between force, mass and the motion of objects. • A. Determine the relationship between speed, velocity and acceleration. • B. Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

Relative Motion/ Reference Point • Motion is defined as an object having a change in position. • But how do you know if something has moved or not? P. 282 • Reference Point- A stationary point of comparison used to measure the distance an object has moved. • Relative Motion- An object’s change in position relative to the reference point.

Distance • Distance is the measurement from one point to another. • Distance may refer to a physical length, a period of time, or an estimation.

Displacement • Displacement is the direction and the distance in an object’s position from its starting and ending points. • Example: Suppose you walked 200 meters East to the park from your house, what would be your displacement? • Example 2: Suppose Dale Jr. drives the Daytona 500. Leaves from the start/finish line, completes the race and crosses the same start/ finish line. What would be his displacement?

Speed • Speed is a measure of the distance an object moves in a given amount of time. • During a typical trip to school, your car will undergo a series of changes in its speed.

Formula for Speed • Speed (m/s)=distance (m) / time (s) s=d t – Average speed: divide the total distance by the total time taken to complete a change in an object position. – Instantaneous speed: Speed of an object at a given instant in time. P. 285

Time v. Distance Graphs • Used to compare the speeds of two or more objects. • Time is plotted on the X-axis. • Distance is plotted on the Y-axis • A straight horizontal line on a speed-time graph means the speed is constant. This means the speed is not changing over time.

Time/Distance Graph

Speed is a rate • A rate is a ratio of two different variables. • Speed is equal to the rate of distance divided by the time it takes to go that distance. • Tim & Moby break it down. . .

Velocity • Velocity is an object’s speed in a particular direction. If the direction changes, the velocity will also change. • Velocity always includes speed and direction.

Speed vs Velocity Let's ask Mr. Panda Bear!

Force • A push or pull that causes an object to move, stop, or change direction • A force will cause an object with mass to accelerate.

Forces can affect motion in several ways: • • • → They can make objects start moving. → They can make objects move faster. → They can make objects move slower. → They can make objects stop moving. → They can make objects change direction. • ***These are ALL forms of acceleration!!

Acceleration & Deceleration • Acceleration is an increase in speed. It is positive acceleration. • Deceleration is a decrease in speed. It is negative acceleration.

Calculating Acceleration (m/s 2) = final speed – initial speed time a= sf – si t 1. Calculate the acceleration of a car whose speed changes from 6 m/s to 12 m/s in 3 s. 2. Calculate the acceleration of a bus whose speed changes from 30 m/s to 10 m/s in 5 s.

Speed & Time Graph

Where is Zero Acceleration?

Acceleration: Video Help • Put the pedal to the medal!

Speed/Acceleration Summarizer • Graphing Activity – Look at the graph and answer the questions in your ISN. § SPEED LAB (OUTSIDE)

Mass & Inertia • Mass is the amount of matter in an object. • Inertia- the tendency of an object to resist a change in its motion.

More on Inertia • As an object’s mass increases…so does it’s inertia. WEAR YOUR SEATBELT!!!! • https: //www. youtube. com/watch? v=d 7 i. YZ Pp 2 z. YY

Momentum • Momentum- A measure of how hard it is to STOP a moving object and it depends on the mass and velocity of the object. • Which would be harder to stop…. – A 68 kg. guy going 10 m/s on a bicycle or a 2 g. bullet fired from a rifle at 1200 m/s? Why ? Momentum = mass X velocity (g or kg x m/s ) = g or kg x m/s

Law of Conservation of Momentum • In any collision between objects, momentum is transferred from one object to another. (example…playing pool or bowling. ) • The total momentum will stay the same unless acted on by an outside force like gravity or friction. • Let’s make predictions based on size and directions: small- big, Big-small, same size

Momentum Simulation • http: //phet. colorado. edu/sims/collisionlab/collision-lab_en. html

Video • Motion & Force