Motion & ForceMotion & Force

~ Review for Unit Test ~~ Review for Unit Test ~

Vocabulary…Know all T-n-T Vocabulary…Know all T-n-T vocabulary and the following:vocabulary and the following:

GravityGravity – A force of attraction between objects that – A force of attraction between objects that is due to their massesis due to their masses

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

WeightWeight – A measure of gravitational force exerted – A measure of gravitational force exerted on an object on an object

Kinetic FrictionKinetic Friction – Friction between MOVING – Friction between MOVING surfacessurfaces

Static FrictionStatic Friction – When the force applied doesn’t – When the force applied doesn’t cause the object to movecause the object to move

1. To calculate speed, 1. To calculate speed, velocity & accelerationvelocity & acceleration

SpeedSpeed = Distance/Time -- or D/T = Distance/Time -- or D/TVelocityVelocity = D/T plus direction = D/T plus directionAccelerationAcceleration = = Change in Velocity Change in Velocity

(Speed)(Speed) Change in TimeChange in Time V2 – V1V2 – V1 Change in TimeChange in TimeProblem on test for each of these…Problem on test for each of these…

Know formulas.Know formulas.

2. Difference between 2. Difference between Speed & VelocitySpeed & Velocity

Speed = D/TSpeed = D/T

Velocity = D/T plus DIRECTIONVelocity = D/T plus DIRECTION

3. Difference between mass 3. Difference between mass and weightand weight

WeightWeight is a measure of is a measure of gravitational forcegravitational force on an object… on an object…Use weight scales to measureUse weight scales to measure

MassMass is the measure of is the measure of mattermatter in in an object ...an object ...

Use balance scales (TBB) to Use balance scales (TBB) to measuremeasure

4. How your weight would 4. How your weight would change if you were on the change if you were on the

moonmoon

The moon has less mass than The moon has less mass than Earth and therefore less Earth and therefore less

gravitational force. Your weight gravitational force. Your weight will be less, and approximately will be less, and approximately

1/6 of your weight on Earth.1/6 of your weight on Earth.

5. When is an object’s 5. When is an object’s velocity constant?velocity constant?

When the object’s speed and/or When the object’s speed and/or direction don’t change. direction don’t change.

6. Objects in a circular 6. Objects in a circular motion…motion…

Such as a windmill, a Ferris Such as a windmill, a Ferris wheel or Earth’s rotation are wheel or Earth’s rotation are always always CHANGING CHANGING direction, direction, therefore their therefore their VELOCITYVELOCITY changes, and they are changes, and they are ACCELERATINGACCELERATING..

7. Graphing Speed7. Graphing Speed

Time on the X axis (horizontal)Time on the X axis (horizontal)

Distance on the Y axis Distance on the Y axis (vertical)(vertical)

8. Graphing Acceleration8. Graphing Acceleration

Change in Change in time time on the on the X axisX axis

Change inChange in VelocityVelocity on theon the Y axis Y axis

9. The difference between 9. The difference between constant, negative and constant, negative and positive accelerationpositive acceleration

ConstantConstant – Speed or direction – Speed or direction doesn’t changedoesn’t change

Negative accelerationNegative acceleration – – Deceleration…a decrease in Deceleration…a decrease in velocityvelocity

Positive accelerationPositive acceleration – Increase in – Increase in accelerationacceleration

10. How it is possible to 10. How it is possible to accelerate at a constant accelerate at a constant

speedspeed

By changing direction, spinning By changing direction, spinning or turningor turning

11. How Net Force is 11. How Net Force is calculatedcalculated

Forces moving in the Forces moving in the same directionsame direction (for (for example a push to the right and a pull to example a push to the right and a pull to the right) are the right) are ADDEDADDED to determine Net to determine Net ForceForce

Forces moving in Forces moving in opposite directionsopposite directions (for example pulling on both sides (for example pulling on both sides during tug-of-war) are during tug-of-war) are SUBTRACTEDSUBTRACTED to determine Net Force to determine Net Force

Problem on the testProblem on the test

12. The difference between 12. The difference between balanced and unbalanced balanced and unbalanced

forcesforces Balanced forces are Balanced forces are equal forcesequal forces

acting on an object and result in a Net acting on an object and result in a Net Force of Ø Newtons.Force of Ø Newtons.

There is There is no motion no motion or or no change in no change in motionmotion when forces are balanced. when forces are balanced.

Unbalanced forces are Unbalanced forces are not equalnot equal and and

motion or a change in motionmotion or a change in motion results.results.

13. Source of Friction13. Source of Friction

When surfaces are in contact and When surfaces are in contact and force is appliedforce is applied

Friction occurs on smooth surfaces -- Friction occurs on smooth surfaces -- just less just less

14. What the amount of 14. What the amount of friction depends onfriction depends on

ForceForce pushing the surfaces pushing the surfaces together and the amount of together and the amount of roughnessroughness of the surfaces of the surfaces

15. The difference between 15. The difference between static friction and kinetic static friction and kinetic

frictionfrictionStatic FrictionStatic Friction – There is – There is no no

movementmovement when force is applied. when force is applied.

Kinetic FrictionKinetic Friction – The friction – The friction between between moving surfacesmoving surfaces

16. Examples of sliding 16. Examples of sliding friction and rolling frictionfriction and rolling friction

Sliding FrictionSliding Friction – Book sliding across – Book sliding across the table; the table;

Rolling FrictionRolling Friction – A pencil rolling across – A pencil rolling across the table. Anything with wheels the table. Anything with wheels rolling on a sidewalk (Skateboard)rolling on a sidewalk (Skateboard)

Usually the force of sliding friction Usually the force of sliding friction is greater than rolling frictionis greater than rolling friction

17. How friction can be 17. How friction can be harmful or helpfulharmful or helpful

HarmfulHarmful – Erosion of topsoil, worn out – Erosion of topsoil, worn out engine parts or overheating engine, engine parts or overheating engine, machines less efficient, worn out machines less efficient, worn out shoes, holes in socks or jeans, etc.shoes, holes in socks or jeans, etc.

HelpfulHelpful – Traction between the – Traction between the highway and car wheels, writing highway and car wheels, writing with a pencil, walking or running, to with a pencil, walking or running, to generate heat or energy, etc.generate heat or energy, etc.

18. Some ways to reduce 18. Some ways to reduce and increase frictionand increase friction

To reduce friction – Using sandpaper to To reduce friction – Using sandpaper to smooth a surface, using oil, wax or smooth a surface, using oil, wax or grease (lubricants), switching from grease (lubricants), switching from sliding to rolling kinetic friction.sliding to rolling kinetic friction.

To increase friction – Apply greater To increase friction – Apply greater force or roughness to the surfaces in force or roughness to the surfaces in contact.contact.

19. The Law of Universal 19. The Law of Universal GravitationGravitation

All objects in the universe attract All objects in the universe attract each other through gravitational each other through gravitational force. The size of the force force. The size of the force depends ondepends on the the massesmasses of the of the objects and the objects and the distancedistance between them.between them.

20. How gravitational force 20. How gravitational force changes changes when mass increases or when mass increases or distance distance increases increasesWhen When mass increasesmass increases – –

Gravitational force increasesGravitational force increases

When When distance increasesdistance increases – – Gravitational force decreasesGravitational force decreases

Distance m, km

Time s, hr

Speed m/s; Km/hr

Velocity m/s West

Acceleration m/s² West1. 40

secondsTimeTime

2. 25 km/hr SpeedSpeed3. 2 m/s SpeedSpeed4. 15 m/s south

VelocityVelocity

5. 5 m/s² north

AcceleratiAccelerationon

6. 100 km DistanceDistance

Units of Expression