# Physics (P2) - Forces

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• Created by: Roma
• Created on: 13-12-13 22:08
What forces do objects always exert on each other?
Equal and opposite forces.
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What is the resultant force?
The single force that has the same effect as all the forces acting on an object.
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When would the resultant force of an object be zero?
If the object is at rest, it will stay at rest. If the object is moving, it will carry on moving at the same speed and in the same direction.
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What does it mean if the resultant force is not zero?
There will be an acceleration in the direction of the force. If the object is at rest, it will accelerate in the direction of the resultant force.
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What happens if there is no acceleration?
The resultant force is zero.
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Why would a big braking time be need for a vehicle.
If a vehicle is travelling at a fast speed, the bigger the deceleration needed to stop it in a particular distance.
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Why is stopping distance?
The distance a vehicle travels during the driver's reaction time (thinking time) plus the distance it travels under the braking force (braking distance).
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How is thinking distance increased?
If the driver is tired or under the influence of drugs or alcohol.
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How can braking time be increased?
Bad weather/poor road condition, the car conditions.
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What happens to a free falling object?
The resultant force acting on it is gravity. It will make an object fall close to the Earth's surface accelerate at about 10m/s squared.
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What happens if the object is on Earth and not falling.
Acceleration is called gravitational field strength (N/Kg).
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What happens when an object falls through a liquid?
The fluid exerts a drag force on the object resisting its motion. The faster the object falls, the bigger the drag force. until it eventually is equal to the weight of the object.
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What is constant velocity?
Terminal velocity.
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What is extension?
The difference between the length of a stretched object, and its original length.
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What is elasticity?
When an object regains its original shape when the forces changing it are removed.
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What does Hooke's Law state?
Extension is directly proportional to the force applied, provided the limit of proportionality is not exceeded.
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What is fuel economy?
Reducing the amount of fuel a vehicle uses to travel a particular distance.
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How can fuel economy on roads be improved?
By reducing speed or making vehicles more streamlined (e.g. fitting a wind deflector).
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Why does skidding happen?
If the brakes of a vehicle are applied too harshly, the wheels lock and slide along the surface, increasing the stopping distance.
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How to anti-skid surfaces work?
They have rougher surfaces, increasing the friction between tyres and the road.
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## Other cards in this set

### Card 2

#### Front

What is the resultant force?

#### Back

The single force that has the same effect as all the forces acting on an object.

### Card 3

#### Front

When would the resultant force of an object be zero?

### Card 4

#### Front

What does it mean if the resultant force is not zero?

### Card 5

#### Front

What happens if there is no acceleration?