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Taken from - Chapter 10, sec. 2.  Your word is Friction.

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Presentation on theme: "Taken from - Chapter 10, sec. 2.  Your word is Friction."— Presentation transcript:

1 Taken from - Chapter 10, sec. 2

2  Your word is Friction.

3  When you ride a sled down a snowy hill, the sled’s motion changes at the top of the hill, down the side and then again at the bottom.  What causes the change in motion?  There are different forces acting on the sled – those forces are gravity which makes the sled speed up - and friction which brings the sled to a stop at the bottom of the hill. Let’s look more at these two forces.

4  Remember - Force is a push or pull on an object that can result in changing that object’s motion.  Remember - The strength of force is measured in the SI Unit called the newton.  Since gravity is a force – it is also measured in newtons.

5  The strength of friction depends on how hard the surface of the object and the surface the object is on push together.  It also depends on the type of surface the object has and the type surface the object is on. ◦ Try this – rub your hands together very lightly and then rub them together with more force – which causes more friction?  When you rub your hands together more forcefully.

6  Friction acts in the direction opposite of the direction of motion. ◦ So when your sled is sliding down the hill, friction is working in an direction up the hill. ◦ Without friction – moving objects would just keep going until they hit something.

7  Static Friction – friction that acts on an object that is not moving or is at rest. ◦ Example: Your desk is sitting on the floor right now and is not moving, so the only type of friction working on your desk is static friction. ◦ In your foldable :  Put the term ‘static friction’ on the outside  Put the definition on the inside flap  Draw a picture on the inside on the part of the paper directly across from the flap.

8  Sliding Friction – friction that occurs when two surfaces slide over each other. ◦ Example: When you push your textbook across your desk you have sliding friction working on both the book and the desk. ◦ In your foldable :  Put the term ‘sliding friction’ on the outside  Put the definition on the inside flap  Draw a picture on the inside on the part of the paper directly across from the flap.

9  Rolling Friction – friction that occurs when an object rolls across another surface. ◦ Example: When you ride a skateboard or bicycle on the road. ◦ In your foldable :  Put the term ‘rolling friction’ on the outside  Put the definition on the inside flap  Draw a picture on the inside on the part of the paper directly across from the flap.

10  Fluid Friction – friction that occurs when a solid object moves through a fluid, such as water, air, or oil. ◦ Example: When you ride a surfboard through an ocean wave. ◦ In your foldable :  Put the term ‘fluid friction’ on the outside  Put the definition on the inside flap  Draw a picture on the inside on the part of the paper directly across from the flap.

11  On a separate sheet of paper and without looking at your foldable/notes - List and describe the 4 types of friction.

12  Your word is Gravity.

13  Gravity is the force that pulls objects toward each other. ◦ The Earth pulls on the moon which keeps the moon in orbit around the Earth. ◦ Gravity also pulls on us to keep us on the Earth.  The two factors that affect gravity are mass and weight.

14  Mass is the amount of matter in an object.  Weight is a measurement of the force of gravity on an object.  Remember – mass does not change from place to place because the amount of matter in an object does not change with location.  Remember – weight does change from place to place, such as here on Earth vs. on the moon, because the force of gravity changes.  The moon has less gravitational pull than the Earth, so an object would weigh less on the moon.

15  In your notebooks – calculate the weight of the following objects based on their given mass: ◦ Notebook – 10 grams ◦ Pencil – 0.5 grams ◦ Desk – 10 kilograms ◦ Textbook – 20 grams ◦ Person – 50 kilograms  You may use a calculator if you have one.

16  Your words are Mass and Weight.

17  Free fall occurs when the only force acting on an object is the force of gravity.  During free fall, gravity is an unbalanced force which causes the object to accelerate.  Because the only force acting on an object in free fall is gravity, all objects in free fall accelerate at the same rate - the rate of acceleration due to gravity.  The rate of acceleration due to gravity is 9.8m/s 2.

18  Objects falling through air experience a type of fluid friction called Air Resistance.  Like all other types of friction – air resistance works in a direction opposite of the falling object. Therefore, air resistance works in an upward direction. ◦ Try this: ◦ Drop a flat piece of paper from a height equal to the height of your desk. Then drop a crumpled sheet of paper from the same height. ◦ Which one experiences the most air resistance?  The flat sheet will experience the most air resistance because it has a larger surface area.

19  We know that falling objects accelerate at the rate due to gravity – 9.8m/s 2.  However, air resistance increases with velocity. ◦ At this point the forces on the falling object will be balanced, meaning there is no longer any acceleration. The object keeps falling but at the a constant rate = no acceleration.  Terminal Velocity is the greatest velocity a falling object reaches. ◦ Terminal velocity is reached when the force of air resistance equals the force of gravity on the object, or the object’s weight.

20  An object that is thrown, instead of dropped straight down, is called a projectile.  Projectile motion describes the motion of a projectile.  NOTE: A projectile and an object dropped straight down will reach the ground at the same time.  This happens because both objects are acted on by the force of gravity in the same way. ◦ See the picture on p. 348 in the textbook.

21  On a separate sheet of paper do the ‘writing in science’ activity on page 348 in your textbook.


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