Forces and MotionForces and Motion

2013 M.B. Pardington, BPS

A force is a…

PUSH PULL

A force can change the motion of an object.

SPEED

DIRECTION

A force can change the motion of an object.

An additional force in the same direction increases the speed

of the object.

Push Push + Push

An additional force in the same direction increases the speed

of the object.

Push Push + Pull

An additional force in the same direction increases the speed

of the object.

Pull Pull + Pull

Opposing forces of equal magnitude acting on an object produce no change in motion.

5 N vs. 5 NCart doesn’t move.

Opposing forces of equal magnitude acting on an object produce no change in motion.

5 N vs. 5 NCart doesn’t move.

Opposing forces of unequal magnitude acting on an object result in a change in motion.

3 N Pull + 5 N Push

NET FORCE 2 N PUSH to the

RIGHT

A change in motion is described as a change in speed

and/or direction of an object.

3 N Pull + 5 N Push

NET FORCE 2 N PUSH to the

RIGHT

BALANCED FORCEA force must be A force must be

balancedbalanced in order to in order to achieve achieve constantconstant speed. speed.

UNBALANCED FORCE

A force must be A force must be unbalancedunbalanced (nonzero net force) in order (nonzero net force) in order

for an object to change for an object to change speed and/or direction.speed and/or direction.

20 N

40 N

UNBALANCED FORCE

A force must be A force must be unbalancedunbalanced (nonzero net force) in order (nonzero net force) in order

for an object to change for an object to change speed and/or direction.speed and/or direction.

20 N

50 N

30 N

UNBALANCED FORCEA change in the mass of the A change in the mass of the object will result in a change object will result in a change in speed and/or direction of in speed and/or direction of the object. Compare these 3 the object. Compare these 3

carts.carts.

UNBALANCED FORCEA change in the mass of the A change in the mass of the object will result in a change object will result in a change in speed and/or direction of in speed and/or direction of the object. Compare these 3 the object. Compare these 3

carts.carts.

UNBALANCED FORCEA change in the mass of the A change in the mass of the object will result in a change object will result in a change in speed and/or direction of in speed and/or direction of

the object. Compare these 3 the object. Compare these 3 carts.carts.

SpeedSpeed is the ratio of Speed is the ratio of

distance covered per unit distance covered per unit of time.of time.

Speed = distance / timeSpeed = distance / time

The cart moved 6 meters per 3 seconds

Speed

The cart moved 6 meters per 3 seconds

Mathematically, that’s 6 / 3 or 6 ÷ 3which equals 2.

So, the cart moved 2 meters per secondor 2 m/sec

FORCE

CONTACTCONTACT NON-NON-CONTACTCONTACT

Contact Force

Contact Force

A contact force contact force is a push or pull that

directly touches the object..

FrictionFriction is a contact force exerted between objects such as:

AIR OBJECTS

WATER

Non-Contact Forces

GRAVITY

MAGNETISM

ELECTRICALCHARGES

Non-Contact Forces

These are pushes and pulls from a distance.

GravityGravityGravity is a force of

attraction between any mass and the matter

near it. The larger the mass of an object, the

greater the gravitational force it exerts on other

objects. For objects For objects on Earth, the pull of on Earth, the pull of

the Earth is the the Earth is the strongest force strongest force acting on them.acting on them.

Gravity““Jupiter is the most Jupiter is the most

massive planet in our massive planet in our Solar System and; Solar System and;

therefore, the therefore, the gravity gravity of Jupiter is the most of Jupiter is the most

intense in the Solar intense in the Solar system. Its system. Its

gravitational pull gravitational pull is is 2.5 times what is 2.5 times what is

here on Earth.”here on Earth.”

http://www.universetoday.com/15110/gravity-of-jupiter/

Gravity

Magnetism

N NS S

Here are “like” charges. Are they showing an attraction or are they

repelling?

Magnetism

N NS S

They are repelling.

Magnetic Repulsion

Magnetism

N NS S

Here are “unlike” charges. Are they showing an attraction or are they

repelling?

Magnetism

N NS S

They are showing an attraction.

Magnetic Attraction

Magnetism

N NS S

The attracting and repelling magnetic forces illustrate non-contact forces.They pull and push without contact.

N NS S

Electrical Charges

The attracting and repelling electrical forces illustrated in

the wind sock demonstration show non-contact forces.They push without

contact.

Bibliographyhttp://powerup.ukpowernetworks.co.uk/media/22576/78.jpg

http://www.clipart.dk.co.uk/DKImages/science/image_science010.jpg

http://www.clipart.dk.co.uk/DKImages/science/image_science009.jpg

http://www.universetoday.com/15110/gravity-of-jupiter/

http://www.mikecurtis.org.uk/images/friction.jpg

http://lvp.lockyersmid.dorset.sch.uk/pluginfile.php/3230/mod_resource/content/0/content/pictures/physical/keyideas/phpkey0005.jpg

http://www.united-states-flag.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/F/L/FLGBDEC1000003637_-00_st-patricks-wind-sock_4.jpg