Forces Flashcards
What are vector quantities?
A vector quantity has a magnitude and direction.
What are examples of vector quantities?
- Force,
- Velocity,
- Displacement,
- Acceleration,
- Momentum.
What are scalar quantities?
A scalar quantity has a magnitude but no direction.
What are examples of scalar quantities?
- Speed,
- Distance,
- Temperature,
- Time
How can two objects have a different velocity but be travelling at the same speed?
- Since speed is a scalar quantity, they can both have the same speed (length of the arrows) but be travelling in a different direction (the direction of the arrow),
- Velocity is vector quantity, this means that two objects moving at the same speed could have different velocities because they are travelling in different directions.
- A negative velocity moving backwards and a positive velocity moving forwards.
What are the two types of forces?
- Contact,
- Non-Contact.
What is a contact force?
A force that acts when two objects touch.
What is non-contact force?
When the objects do not need to be touching for a force to act.
What are some examples of a contact forces?
- Friction,
- Air resistance,
- Tension
What area some examples of non-contact forces?
- Magnetic forces,
- Gravitational force,
- Electrostatic forces.
What is an interaction pair?
A pair of forces that act on two objects, these forces act with equal strength in opposite directions.
What is gravity?
- A force that every mass has, it attracts other masses towards it.
- It is only really noticeable on very large masses such as planets.
What are the effects of the Earth’s gravity?
- It makes all masses fall towards the ground,
- It gives everything a weight.
What is the difference between mass and weight?
- Mass is the quantity of matter in a body, weight is the force applied on a mass because of gravity.
- The mass of an object is always the same, however, weight will change depending on the gravitation field strength.
- For example, of earth, the gravity is 9.8 kg/NM but on the moon it is much less so we have less weight on the moon than on Earth.
What is the relationship between mass and weight?
They are directly proportional,
weight = mass x gravity x height
What do arrows show in a free body diagram?
The strength and direction of a force.
What is the resultant force?
- The overall force of an object*
- In any object, when there is a force acting, there will always be one one acting in the opposite direction as well,
- The resultant force, subtracts the smallest force from the largest and shows the force in the stronger direction with an arrow in a free body diagram.,or as a value in Newtons.
What happens when force moves an object through a distance?
Energy is transferred and work is done on the object.
What happens when you push an object over a carpet (in terms of forces applied and energy transfer)?
- You are applying force and working against the friction that the carpet is applying to the object.
- Energy is transferred to the objects kinetic energy store because it moves.
- Some energy is also transferred to the thermal store because of the friction, this causes the object to heat.
What is the equation involving work done, distance and force?
W = Fs
Work done = force x distance
J = N x m
How do you find the resultant force of an object that has a force acting horizontal and vertical?
- First draw the vertical force to scale (3N = 3cm),
- Then draw the horizontal force to scale at the end of the vertical force,
- Draw a hypotenuse and find the length, that is the force in newtons,
- Find the angle a well and write the answer as:
(Force) (Bearing)
What does it mean if an object is at equilibrium?
- The forces on either side of the object are equal,
- The object is either stationary (if it wasn’t moving originally),
- Or the object is moving at a constant velocity (if it was moving originally).
What is magnitude?
The size of a quantity is it’s magnitude
What is displacement?
This is distance without change.
What is Newton’s third law?
A law that states when two objects interact with each other, they exert equal and opposite forces on each other.
What is the unit of force?
Newtons
What happens to the force when a car moves?
The force of friction of the road on the tyre is in the forward direction
The force of the friction of the tyre on the road is in the reverse direction these two forces are equal and opposite.
What is Newton’s first law of motion?
If the forces acting on an object are balanced the resultant force on the object is zero. And if:
The object is at rest, it stays stationary
The object is moving, it keeps moving with the same speed and in the same direction.
What is an unbalanced force?
This is where the resultant force on an object is not zero, the movement of the object will depend on the size direction and resultant force
How can the moment of the force be increased on a spanner?
Increase the size of the force
Using a longer handle on the spanner
What is the load?
This is the weight of the object
What is the effort?
This is the force you apply
What is the pivot/fulcrum?
This is the point where something turns
What is a lever?
It is something that includes a pivot which reduces the amount of effort you have to achieve to lift or move the load
What is the equation for moment of force?
Moment=force*perpendicular distance from the line of action of the force to the pivot
Give examples of force multipliers
Gears
Levers
Why do you use a lever?
It multiplies the force as you get further away from the pivot the more the force
Becomes
Give some examples of levers?
Bottle opener
A pair of scissors
What is a gear?
Gears multiply the moment of a turning effect by using a smaller gear to turn a larger gear.
What happens when a large gear turns a small one and vise vera?
- When a large gear turns a small gear, the turning effect is reduced (force applied) but the speed of the little gear is increased, so both gears have equal moment.
- When a smaller gear turns a larger gear, the turning effect increases, but the speed reduces, so both gears have equal moment.
What is the centre of mass?
The centre of mass of an object is the point at which its mass can be thought of as being concentrated
What is suspended equilibrium?
When you suspend an object the centre of mass will always come to rest with its centre of mass directly below the point of suspension
How to you find the centre of mass on a 2D object?
You would draw all the lines of symmetry and find the point where they all cross that is the centre of mass.
How do you find the centre of mass of a irregular shape?
- Put a hole in one corner of the card and suspend the card from a rod
- Use a plumbline to draw a vertical line on the card from the rod
- Repeat the procedure, hanging the card from a different corner
The point where the two lines meet is the cards centre of mass.
What determines the moment on a see saw?
The weight of the person and the distance from the pivot.
W1D1=W2D2
Why does an object stretch, bend or compress?
Because more than one force is acting on the object in different directions,
- For example, a spring would bend if there are forces pushing from one side at the top and another force pushing from the opposite side at the bottom.
Why does an object not stretch, bend or compress when force is only applied from one direction?
Because the object would simply be moved instead of bending/ stretching since the object does not have forces acting against each other.
What is an elastic object?
Any object that is elastically deformed.