# Resultant Forces

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• Created by: Lotto65
• Created on: 12-12-15 17:50
What is the unit of force?
Newtons (N)
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What is the rule of force when objects interact with each other?
The forces they exert on each other are equal and opposite
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What are the forces when a book is placed on a table?
Book exerts weight on the table; Table exerts reaction force on the book
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What forces are involved when a car is driven forwards?
Force of tyre on road pushes backwards; Force of road on tyre pushes forwards
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When a sprinter starts running, the action force is the one of each running shoe on the starting blocks. What is the reaction force and in which direction?
Starting blocks on the running shoe in the forwards direction
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What is a resultant force?
A single force that has the same effect as all the forces acting on an object
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What happens if the resultant force on a moving object is zero?
Object moves at the same speed in the same direction
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What happens if the resultant force on an object is zero when it is stationary?
It stays stationary
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What happens if the resultant force is not zero and the object is stationary?
It accelerates in the direction of the force
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What happens if the resultant force is not zero and the object is moving in the same direction as the force?
It accelerates in that direction
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What happens if the resultant force is not zero and the object is moving in the opposite direction?
It decelerates
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I have two forces named A and B, if they both act in the same direction, give an equation for the resultant force
A+B
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I have two forces named A and B, if they act in opposite directions, give an equation for the resultant force
A-B if A is larger or B-A if B is larger
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What is deceleration?
Negative acceleration
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A resultant force always causes...
Acceleration
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If an object does not accelerate, what is the resultant force?
Zero
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What is acceleration?
A change in velocity
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If an object has changed direction but is still at a constant speed, has it accelerated?
Yes because it has changed direction
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Give the equation symbol for resultant force
F
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Mass is always measured in...
Kilograms
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The greater the resultant force on an object...
The greater its acceleration
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The greater the mass of an object...
The greater the force needed to make it accelerate by a certain amount
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In what direction does gravity or weight act in?
Downwards
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In what direction does a reaction force on the surface act in?
Upwards
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What does thrust, push or pull do to an object?
Speeds it up
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What does drag, air resistance or friction do to an object?
Slows it down
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Give two things that create thrust, push or pull
An engine or rocket
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How many forces are always acting on an object?
At least two
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How do you work out the resultant force on an object if the forces are not on the same line?
Draw a scale drawing; join up the two lines given and measure with a ruler-draw to a sensible scale
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I have two objects, one is 60kg and the other is 50kg and they are going at 30mph given the same force. Which one accelerates more and why?
The 50kg object because it has a smaller mass so not as much force is needed to accelerate the same amount
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## Other cards in this set

### Card 2

#### Front

What is the rule of force when objects interact with each other?

#### Back

The forces they exert on each other are equal and opposite

### Card 3

#### Front

What are the forces when a book is placed on a table?

### Card 4

#### Front

What forces are involved when a car is driven forwards?

### Card 5

#### Front

When a sprinter starts running, the action force is the one of each running shoe on the starting blocks. What is the reaction force and in which direction?