Motion & Force ~ Review for Unit Test ~

Vocabulary…Know all T-n-T vocabulary and the following: Gravity – A force of attraction between objects that is due to their masses Law of Universal Gravitation- All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between them Weight – A measure of gravitational force exerted on an object Kinetic Friction – Friction between MOVING surfaces Static Friction – When the force applied doesn’t cause the object to move

1. To calculate speed, velocity & acceleration Speed = Distance/Time -- or D/T Velocity = D/T plus direction Acceleration = Change in Velocity (Speed) Change in Time Change in Time V2 – V1 V2 – V1 Change in Time Change in Time Problem on test for each of these… Know formulas.

2. Difference between Speed & Velocity Speed = D/T Velocity = D/T plus DIRECTION

3. Difference between mass and weight Weight is a measure of gravitational force on an object…Use weight scales to measure Mass is the measure of matter in an object... Use balance scales (TBB) to measure Use balance scales (TBB) to measure

4. How your weight would change if you were on the moon The moon has less mass than Earth and therefore less gravitational force. Your weight will be less, and approximately 1/6 of your weight on Earth.

5. When is an object’s velocity constant? When the object’s speed and/or direction don’t change. When the object’s speed and/or direction don’t change.

6. Objects in a circular motion… Such as a windmill, a Ferris wheel or Earth’s rotation are always CHANGING direction, therefore their VELOCITY changes, and they are ACCELERATING. Such as a windmill, a Ferris wheel or Earth’s rotation are always CHANGING direction, therefore their VELOCITY changes, and they are ACCELERATING.

7. Graphing Speed Time on the X axis (horizontal) Distance on the Y axis (vertical)

8. Graphing Acceleration Change in time on the X axis Change in Velocity on the Y axis

9. The difference between constant, negative and positive acceleration Constant – Speed or direction doesn’t change Negative acceleration – Deceleration…a decrease in velocity Positive acceleration – Increase in acceleration

10. How it is possible to accelerate at a constant speed By changing direction, spinning or turning By changing direction, spinning or turning

11. How Net Force is calculated Forces moving in the same direction (for example a push to the right and a pull to the right) are ADDED to determine Net Force Forces moving in opposite directions (for example pulling on both sides during tug-of- war) are SUBTRACTED to determine Net Force Problem on the test

12. The difference between balanced and unbalanced forces Balanced forces are equal forces acting on an object and result in a Net Force of Ø Newtons. Balanced forces are equal forces acting on an object and result in a Net Force of Ø Newtons. There is no motion or no change in motion when forces are balanced. There is no motion or no change in motion when forces are balanced. Unbalanced forces are not equal and motion or a change in motion results.

13. Source of Friction When surfaces are in contact and force is applied Friction occurs on smooth surfaces -- just less

14. What the amount of friction depends on Force pushing the surfaces together and the amount of roughness of the surfaces

15. The difference between static friction and kinetic friction Static Friction – There is no movement when force is applied. Kinetic Friction – The friction between moving surfaces

16. Examples of sliding friction and rolling friction Sliding Friction – Book sliding across the table; Rolling Friction – A pencil rolling across the table. Anything with wheels rolling on a sidewalk (Skateboard) Usually the force of sliding friction is greater than rolling friction

17. How friction can be harmful or helpful Harmful – Erosion of topsoil, worn out engine parts or overheating engine, machines less efficient, worn out shoes, holes in socks or jeans, etc. Helpful – Traction between the highway and car wheels, writing with a pencil, walking or running, to generate heat or energy, etc.

18. Some ways to reduce and increase friction To reduce friction – Using sandpaper to smooth a surface, using oil, wax or grease (lubricants), switching from sliding to rolling kinetic friction. To increase friction – Apply greater force or roughness to the surfaces in contact.

19. The Law of Universal Gravitation All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between them. All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between them.

20. How gravitational force changes when mass increases or distance increases When mass increases – Gravitational force increases When distance increases – Gravitational force decreases

Distance m, km Time s, hr Speed m/s; Km/hr Velocity m/s West Acceleration m/s² West secondsTime km/hrSpeed 3. 2 m/sSpeed m/s southVelocity 5. 5 m/s² northAcceleration kmDistance Units of Expression