Forces, Movement And Shape Flashcards
What does a vector quantity have?
Magnitude and direction
What does a scalar quantity have ?
Magnitude only
What can scalar quantities never be ?
Negative
What can forces do to an object to they way it moves?
- objects can accelerate or decelerate
* objects can change direction
What can forces do to objects to change their size ?
- objects can be stretched
* objects can be squeezed
What is the normal reaction force ?
When an object rests on a solid if feels a reaction force at 90° to the surface
Where does upthrust always occur ?
In a fluid
What is thrust ?
Thrust is a reaction force
• it occurs when mass is pushed out the back of something causing the object to move toward
• eg rocket
What is an electrostatic force ?
Similar charges repel and opposite charges attract
What is an magnetic force ?
Like poles repel, opposite poles attract
What always happens to weight ?
Weight is always drawn down from the centre of gravity
What is the unit for mass?
Kg
What is the unit of weight?
N
What depends on the strength of the gravitational field ?
Weight, mass doesn’t change
What happens to any two objects that have mass?
They will attract each other, the more massive the object the bigger the gravitational force
Relation between weight mass and gravitational field strength
Weight = mass x gravitational
What is the gravitational field strength on earth?
10 N/kg
What is newtons second law?
In the presence of a resultant force a body experiences an acceleration
What does resultant mean ?
Overall
What overall force does a stationary object have?
No overall force
What is the equation linking acceleration, force and mass ?
Acceleration = force/mass
If acceleration is equal to force, what is mass?
Constant mass
What is force proportional to ?
Acceleration and acceleration is proportional to force
Describe terminal velocity
- when object starts falling it is accelerating as weight is much greater than air resistance
- The forces start to balance out however still accelerating but not as quickly
- when weight is equal to air resistance the object stops accelerating and falls at a constant speed, this is called terminal velocity
What is stopping distance made up of?
- thinking distance
* braking distance
What is thinking distance?
It is the distance travelled whilst the body is reacting to the message it receives from the brain
What is braking distance?
It is the distance travelled whilst the car is decelerating to a stop
How does the thinking distance increase?
It increases linearly
How does braking distance increases?
It increases exponentially
What does braking distance depend on?
Speed squared
What affects braking distance?
• vehicle condition - brake pads/tyres are worn, braking will take longer
• road condition - rain or ice on the road surface will increase braking distance
• mass of car - heavier car=take longer to stop
( only use if others can’t be used )
What affects thinking distance ?
• age • drugs/alcohol • fatigue • distraction - they all increase reaction time
What is the moment of a force?
It Is a measure of the forces turning effect
What will forces with a big moment have ?
Larger turning effect
What an two identical forces have?
They can have entirely different moments
What is the equation linking force, moment and perpendicular distance from pivot ?
Moment = force x distance
What is the principle of moment ?
In equilibrium moments anticlockwise equals moments clockwise
What is the equation linking 2 forces and 2 perpendicular distances ?
F1d1 = F2d2
What is the centre of mass ?
It is an imaginary point through which all the mass of an object can be said to act
What will an object do around the centre of mass ?
Rotate
what will cause a object to fall over?
When an object’s centre of mass falls outside its base the object will topple over
What is hooks law?
That the extension of a spring is proportional to the load
What also about hooks law but only at the beginning?
A wire and rubber band
What equation links force, spring constant and extension ?
Force=spring constant x extension
What is the spring constant measured in ?
Newtons per metre (N/m)
What is the spring constant ?
The “stiffness” of a spring
What does a large spring constant indicate and what does a small spring constant indicate ?
- Large spring constant = very stiff spring
* small spring constant = very loose spring
What happens when you stretch a spring to its elastic limit ?
It won’t go back to its original shape
What is elastic behaviour ?
When you stretch and object with this behaviour it will return to its original shape
