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Force

This document provides information about force and motion. It defines a force as a push or pull and notes that all forces have magnitude and direction. It then gives several examples of the effects of different forces, such as an arrow hitting a target. The document discusses that a force can change an object's shape, size, and motion. It also defines types of motion, speed, velocity, acceleration, and summarizes Newton's Three Laws of Motion.

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Force and Motion Review
• A force is simply a push or a pull. • All forces have both Magnitude and direction. • It is an action that can change the shape ,size and motion of a object.
The following examples show the different effects of forces. An arrow hits into a target. (The arrow pushes into the target)
An athlete reaches the finishing line and the finishing line is being stretched. (The athlete pushes the finishing line and the finishing line is being pulled)
A basketball goes through the net. (The basketball pushes through the net)
What will happen when you step on the step-pad ? Yes. The lid will open. Are you pushing or pulling the step- pad? Well done! You are pushing the step- pad.
What is the man trying to do? Yes. He is trying to drill a hole. Is the drill bit pushing or pulling itself into the wood? Well done! The drill bit is pushing itself into the wood.
- playing a guitar - scrubbing the floor - sawing wood - rowing a boat • A pull is when we apply a force to move an object towards our body • A force to move an object away from our bodies FORCE A force is a push or a pull or both. A force cannot be seen but we can feel and observe the effects of the force. PUSH PULL COMBINATION OF PUSH AND PULL
Stops a moving object or makes a stationary object moves Change the speed of a moving object Change the direction of a moving object Changes the shape permanently Changes the shape temporarily EFFECTS OF A FORCE
Stretch a rubber band After An object that will return to its original shape and size after being squeezed, pressed, twisted and stretched is elastic After After Press a sponge Squeeze a spring
Drop a glass After After Tear a piece of paper After Crush an empty can An object that will not return to its original shape and size after being squeezed, pressed, twisted and stretched is inelastic
A solid cannot be compressed or stretched!! IMPORTANT POINT EXPLANATION The shape of a solid object changes when a force is applied to it whether it’s temporarily or permanently Example: crushing a can – changes the shape permanently
when a force is applied in the opposite direction (or different direction), the moving object will change its moving direction
Misconception? A force is needed to keep an object moving with a constant speed Explanation: You do not need forces to move at a steady speed but if you keep the same speed yet change direction, like a moon around a planet, then you have a force acting on you anyway An object will move faster when a force is applied It moves in the same direction as the applied force
• A stationary ball will move when it is kicked • Moves in the same direction as the applied force •The moving ball will stop when an equal force is applied in the opposite direction of its motion
What happens when a force is applied? The stationary object moves
What happens when a force is applied? The speed of the object increases
What happens when a force is applied? The object changes direction
What happens when a force is applied? The moving object stops moving.
What happens when a force is applied? The shape of the object changes.
Effects of forces 1. Force can move a stationary object. 2. Force can change the speed of a moving object. 3. Force can stop a moving object. 4. Force can change direction of a moving object. 5. Force can change the shape of an object.
NET FORCES When two or more forces are combined!
Some tips: 1. Forces in the same direction- add the two forces together. + = 1. Forces in different directions- subtract the two and figure out which direction was the stronger of the two. - =
Balanced vs. unbalanced forces • Unbalanced: when the net force on an object is not zero. These produce a change in motion. • Balanced: when the net force on an object equals zero. These do NOT produce change in motion.
Balanced Force Equal forces in opposite directions produce no motion
Unbalanced Forces Unequal opposing forces produce an unbalanced force causing motion
What is motion? • When an object changes position over time when compared with a reference point we say that the object is in motion.
What is motion? • An object is in motion when it is continuously changing its position based on a reference point and as observed by a person or a device. • Ex: A car from one place to another…
4 General types of motion • linear motion- straght like example running • angular motion- when you rotate you hips for example situps • general motion- when you use both linear and angular motion for example cycling going in straight lines but legs rotating. • projective motion- flight path. long jump,lob in tennis
6 types of mechanical motion 1. Linear motion is the most basic of all motions. Uninterrupted objects will continue to move in a straight line indefinitely. Linear motion is measured in two parts. Speed, and direction. Together these make up the velocity. 2. Reciprocating motion is back and forth motion.
3. Rotary motion is motion in a circle. 4. Oscillation is back and forth motion about a pivot point.
5. Intermittent motion is motion which starts and stops regularly. 6. Irregular motion is motion which has no obvious pattern to its movement.
Speed • The rate at which an object moves. • Depends on distance traveled and the time it takes to travel that distance.
Speed Formula Average speed = total distance total time
Velocity •The speed of an object in a particular direction ***Don’t confuse this with speed…they don’t mean the same thing!!
• Velocity must ALWAYS include a direction Ex: an airplane’s velocity might be 600 km/h south
•Velocity changes as speed OR direction changes
Resultant Velocity. •SAME DIRECTION: add the two velocities together. •DIFFERENT DIRECTION: subtract the two velocities.
Acceleration •The rate at which velocity changes. •To change velocity (change speed or direction or BOTH) • BrainPop: Acceleration video clip
• It is not just HOW MUCH velocity changes, but it is also HOW FAST it changes. • The faster velocity changes, the greater the acceleration is.
Acceleration Formula Acceleration= final velocity – starting velocity time it takes to change velocity • Velocity is expressed in meters per second (m/s) and time is expressed in seconds (s), so acceleration is expressed in meters per second per second (m/s/s)
Newton’s Laws of Motion BrainPop: Newton’s Laws of Motion video clip 1 2 3
Newton’s First Law (law of inertia) An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force. 1
Newton’s First Law (law of inertia) • Mass (kg)is the measure of the amount of matter in an object. • INERTIA is a property of an object that describes how much it will resist change to the motion of the object • More mass an object has means more inertia the object will have.
Newton’s first law
Newton’s Second Law Force equals mass times acceleration. 2
Newton’s Second Law Force = Mass x Acceleration • Force is measured in Newtons • ACCELERATION of GRAVITY Earth) = 9.8 m/s2 • WEIGHT is a measure of the force of gravity on the mass of an object • Weight (force) = mass x gravity (Earth) • BrainPop: Gravity video clip
This will help up remember: Newton’s Second Law video clip
Newton’s Third Law For every action there is an equal and opposite reaction. 3
Newton’s 3rd Law • For every action there is an equal and opposite reaction. Book to earth Table to book
Think about it . . . What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).
Action: earth pulls on you Reaction: you pull on earth Action and Reaction on Different Masses Consider you and the earth
Action: tire pushes on road Reaction: road pushes on tire
Action: rocket pushes on gases Reaction: gases push on rocket
This will help up remember: Newton’s Third Law video clip
Force is a property of an object. An object has force and when it runs out of force it stops moving EXPLANATION an object at rest or in motion will remain in that state unless an external force is applied to the object Newton 1st Law
Force
Force