friction 4/26/2017 learning outcome: starter:
DESCRIPTION
Wednesday, 26 April 2017Wednesday, 26 April 2017TRANSCRIPT
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FRICTION
Learning Outcome: Explain how the type of surface affects friction Explain how forces affect the motion of an object
Starter:Can you think of a situation where……..1)There is lots of friction2)There is only a little friction3)Where friction can be useful4)Where friction is not useful
05/03/23
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Wednesday 3 May 2023
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Wednesday 3 May 2023
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Friction always tries to slow moving objects down – it opposes motion. Frictional forces occur when two touching surfaces move past each other, in this case the box moving across the ground.
FRICTION AND MOTION
Friction also occurs when things move through air. This is called air resistance.
pull of rope on boxfriction
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Label all sources of friction acting on this bike.
WHAT ARE THE SOURCES OF FRICTION?
pedalbearing
links inchain
tyre androad
airresistance
brake pad
wheelbearing
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FRICTION EXPERIMENT
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Friction is a very important force for the movement of cars. It acts in the opposite direction to the movement of the car.
CARS STOPPING
The time it takes for a car to brake is affected by the frictional forces between the car’s tyres and the road surface.
thrust from engine friction
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EFFECTS OF FRICTIONAL FORCES
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HOW DOES A PLANE TAKE-OFF?
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What forces are acting on the fish?
FORCES IN WATER
Upthrust is a force that pushes objects upwards in a liquid or a gas. This balances the weight of the fish, and is also known as buoyancy.
In order to move forward, the fish uses its tail to produce thrust. This force drives it through the water and is always opposed by friction.
thrust friction
weight
upthrust
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REPRESENTING FORCES
A force is a vector quantity. It always has a size (magnitude) and
direction. We represent the force using an arrow
the length of the arrow represents the size of the force
the direction of the arrow represents the direction of the force.
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TUG OF WAR
Objects can have more than one force acting on them
These forces can act in different directions The forces can be balanced or unbalanced
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WHAT COULD A CAR BE DOING?
1) Accelerating2) Decelerating3) Constant speed4) Stationary
States of motion
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BALANCED AND UNBALANCED FORCES –
and the object is stationary, it will remain stationary and the object is moving, it will continue to move at
the same speed and in a straight line.
If the forces are unbalanced, two things can happen:
If the forces on an object are balanced:
In other words, the object will continue to do what it is already doing without any change.
The speed can change - This is called acceleration or decceleration. The direction of motion can change.
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Accelerating
Constant speed
Decelerating
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IN WHAT OTHER STATE OF MOTION WOULD THE FORCES BE BALANCED?
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The resultant force is calculated by working out the difference between opposing forces in each direction.What is the resultant force on this truck?
The sum effect of more than one force is called the resultant force.
A resultant force of 100 N is accelerating the truck.
RESULTANT FORCE
500 N400 N
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FORCE PAIRS
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500 N 500 N
Imagine a car travelling at a constant speed of 50 km/h.
BALANCED AND UNBALANCED FORCES
The engine provides sufficient force to balance all the frictional forces that are acting to decrease the speed.
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20 N
1. What is the resultant force on the satellite?
Resultant force = 20 N – 10 N= 10 N down
The satellite will accelerate downwards.
RESULTANT FORCES – QUESTION 1
5 N 5 N
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5 N
2. What is the resultant force on the bird?
5 N 5 N
The forces acting in each direction horizontally are equal in size, so there is no resultant force in this direction.
Resultant force = 5 N – 5 N = 0 N
RESULTANT FORCES – QUESTION 2
The vertical forces are not balanced, the bird will accelerate in a downwards direction.Resultant force = 5 N – 0
N = 5 N down
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The vertical forces are equal in size and opposite in direction so there is no resultant force in the vertical direction. The horizontal forces are not balanced, so the yacht will accelerate to the right.
10 N
13 N
3. What is the resultant force on the yacht?
10 N
10 N
Resultant force = (20 N +10 N) – 13 N = 17 N right
RESULTANT FORCES – QUESTION 3
20 N
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UPTHRUST QUIZ
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FORCES – SUMMARY